Quercetin improves epithelial regeneration from airway basal cells of COPD patients

BACKGROUND

Airway basal cells (BC) from patients with chronic obstructive pulmonary disease (COPD) regenerate abnormal airway epithelium and this was associated with reduced expression of several genes involved in epithelial repair. Quercetin reduces airway epithelial remodeling and inflammation in COPD models, therefore we examined whether quercetin promotes normal epithelial regeneration from COPD BC by altering gene expression.

METHODS

COPD BC treated with DMSO or 1 µM quercetin for three days were cultured at air/liquid interface (ALI) for up to 4 weeks. BC from healthy donors cultured at ALI were used as controls. Polarization of cells was determined at 8 days of ALI. The cell types and IL-8 expression in differentiated cell cultures were quantified by flow cytometry and ELISA respectively. Microarray analysis was conducted on DMSO or 1 µM quercetin-treated COPD BC for 3 days to identify differentially regulated genes (DEG). Bronchial brushings obtained from COPD patients with similar age and disease status treated with either placebo (4 subjects) or 2000 mg/day quercetin (7 subjects) for 6 months were used to confirm the effects of quercetin on gene expression.

RESULTS

Compared to placebo-, quercetin-treated COPD BC showed significantly increased transepithelial resistance, more ciliated cells, fewer goblet cells, and lower IL-8. Quercetin upregulated genes associated with tissue and epithelial development and differentiation in COPD BC. COPD patients treated with quercetin, but not placebo showed increased expression of two developmental genes HOXB2 and ELF3, which were also increased in quercetin-treated COPD BC with FDR < 0.001. Active smokers showed increased mRNA expression of TGF-β (0.067) and IL-8 (22.0), which was reduced by 3.6 and 4.14 fold respectively after quercetin treatment.

CONCLUSIONS

These results indicate that quercetin may improve airway epithelial regeneration by increasing the expression of genes involved in epithelial development/differentiation in COPD.

TRIAL REGISTRATION

This study was registered at ClinicalTrials.gov on 6-18-2019. The study number is NCT03989271.

SARS-CoV-2 BNT162b2 vaccine-induced humoral response and reactogenicity in individuals with prior COVID-19 disease

BACKGROUND

Most individuals with prior COVID-19 disease manifest long-term protective immune responses against reinfection. Accordingly, we tested the hypothesis that humoral immune and reactogenicity responses to a SARS-CoV-2 mRNA vaccine differ in individuals with and without prior COVID-19 disease.

METHODS

Health care workers (n = 61) with (n = 30) and without (n = 31) prior COVID-19 disease received two 30 μg doses of Pfizer BNT162b2 vaccine 3 weeks apart. Serum IgG antibody against the spike receptor-binding domain; serum neutralizing activity; and vaccine reactogenicity were assessed longitudinally every 2 weeks for 56 days after the first injection.

RESULTS

The COVID-19 group manifested more rapid increases in spike IgG antibody and serum neutralizing activity after the first vaccine dose but showed little or no increase after the second dose compared with the infection-naive group. In fact, spike IgG was at its maximum level after the first dose in 36% of the COVID-19 group versus 0% of the infection-naive group. Peak IgG antibody levels were lower but appeared to fall more slowly in the COVID-19 group versus the infection-naive group. Finally, adverse systemic reactions, e.g., fever, headache, and malaise, were more frequent and lasted longer after both the first and second injection in the COVID-19 group than in the infection-naive group.

CONCLUSION

Individuals with prior COVID-19 disease demonstrate a robust, accelerated humoral immune response to the first dose but an attenuated response to the second dose of BNT162b2 vaccine compared with controls. The COVID-19 group also experienced greater reactogenicity. Humoral responses and reactogenicity to BNT162b2 differ qualitatively and quantitatively in individuals with prior COVID-19 disease compared with infection-naive individuals.

FUNDING

This work was supported by Temple University institutional funds.

Astegolimab (anti-ST2) efficacy and safety in adults with severe asthma: A randomized clinical trial

BACKGROUND

The IL-33/ST2 pathway is linked with asthma susceptibility. Inhaled allergens, pollutants, and respiratory viruses, which trigger asthma exacerbations, induce release of IL-33, an epithelial-derived "alarmin." Astegolimab, a human IgG₂ mAb, selectively inhibits the IL-33 receptor, ST2. Approved biologic therapies for severe asthma mainly benefit patients with elevated blood eosinophils (type 2-high), but limited options are available for patients with low blood eosinophils (type 2-low). Inhibiting IL-33 signaling may target pathogenic pathways in a wider spectrum of asthmatics.

OBJECTIVES

This study evaluated astegolimab efficacy and safety in patients with severe asthma.

METHODS

This double-blind, placebo-controlled, dose-ranging study (ZENYATTA [A Study to Assess the Efficacy and Safety of MSTT1041A in Participants With Uncontrolled Severe Asthma]) randomized 502 adults with severe asthma to subcutaneous placebo or 70-mg, 210-mg, or 490-mg doses of astegolimab every 4 weeks. The primary endpoint was the annualized asthma exacerbation rate (AER) at week 54. Enrollment caps ensured ∼30 patients who were eosinophil-high (≥300 cells/μL) and ∼95 patients who were eosinophil-low (<300 cells/μL) per arm.

RESULTS

Overall, adjusted AER reductions relative to placebo were 43% (P = .005), 22% (P = .18), and 37% (P = .01) for 490-mg, 210-mg, and 70-mg doses of astegolimab, respectively. Adjusted AER reductions for patients who were eosinophil-low were comparable to reductions in the overall population: 54% (P = .002), 14% (P = .48), and 35% (P = .05) for 490-mg, 210-mg, and 70-mg doses of astegolimab. Adverse events were similar in astegolimab- and placebo-treated groups.

CONCLUSIONS

Astegolimab reduced AER in a broad population of patients, including those who were eosinophil-low, with inadequately controlled, severe asthma. Astegolimab was safe and well tolerated.

DJ-1 Modulates Nuclear Erythroid 2-Related Factor-2-Mediated Protection in Human Primary Alveolar Type II Cells in Smokers

Cigarette smoke (CS) is a main source of oxidative stress and a key risk factor for emphysema, which consists of alveolar wall destruction. Alveolar type (AT) II cells are in the gas exchange regions of the lung. We isolated primary ATII cells from deidentified organ donors whose lungs were not suitable for transplantation. We analyzed the cell injury obtained from nonsmokers, moderate smokers, and heavy smokers. DJ-1 protects cells from oxidative stress and induces nuclear erythroid 2-related factor-2 (Nrf2) expression, which activates the antioxidant defense system. In ATII cells isolated from moderate smokers, we found DJ-1 expression by RT-PCR, and Nrf2 and heme oxygenase (HO)-1 translocation by Western blotting and immunocytofluorescence. In ATII cells isolated from heavy smokers, we detected Nrf2 and HO-1 cytoplasmic localization. Moreover, we found high oxidative stress, as detected by 4-hydroxynonenal (4-HNE) (immunoblotting), inflammation by IL-8 and IL-6 levels by ELISA, and apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay in ATII cells obtained from heavy smokers. Furthermore, we detected early DJ-1 and late Nrf2 expression after ATII cell treatment with CS extract. We also overexpressed DJ-1 by adenovirus construct and found that this restored Nrf2 and HO-1 expression and induced nuclear translocation in heavy smokers. Moreover, DJ-1 overexpression also decreased ATII cell apoptosis caused by CS extract in vitro. Our results indicate that DJ-1 activates the Nrf2-mediated antioxidant defense system. Furthermore, DJ-1 overexpression can restore the impaired Nrf2 pathway, leading to ATII cell protection in heavy smokers. This suggests a potential therapeutic strategy for targeting DJ-1 in CS-related lung diseases.

Secretion of the endoplasmic reticulum stress protein, GRP78, into the BALF is increased in cigarette smokers

Background

Identification of biomarkers of cigarette smoke –induced lung damage and early COPD is an area of intense interest. Glucose regulated protein of 78 kD (i.e., GRP78), a multi-functional protein which mediates cell responses to oxidant stress, is increased in the lungs of cigarette smokers and in the serum of subjects with COPD. We have suggested that secretion of GRP78 by lung cells may explain the increase in serum GRP78 in COPD. To assess GRP78 secretion by the lung, we assayed GRP78 in bronchoalveolar lavage fluid (BALF) in chronic smokers and non-smokers. We also directly assessed the acute effect of cigarette smoke material on GRP78 secretion in isolated human airway epithelial cells (HAEC).

Methods

GRP78 was measured in BALF of smokers (S; n = 13) and non-smokers (NS; n = 11) by Western blotting. GRP78 secretion by HAEC was assessed by comparing its concentration in cell culture medium and cell lysates. Cells were treated for 24 h with either the volatile phase of cigarette smoke (cigarette smoke extract (CSE) or the particulate phase (cigarette smoke condensate (CSC)).

Results

GRP78 was present in the BALF of both NS and S but levels were significantly greater in S (p = 0.04). GRP78 was secreted constitutively in HAEC. CSE 15% X 24 h increased GRP78 in cell-conditioned medium without affecting its intracellular concentration. In contrast, CSC X 24 h increased intracellular GRP78 expression but did not affect GRP78 secretion. Brefeldin A, an inhibitor of classical Golgi secretion pathways, did not inhibit GRP78 secretion indicating that non-classical pathways were involved.

Conclusion

The present study indicates that GRP78 is increased in BALF in cigarette smokers; that HAEC secrete GRP78; and that GRP78 secretion by HAEC is augmented by cigarette smoke particulates. Enhanced secretion of GRP78 by lung cells makes it a potential biomarker of cigarette smoke–induced lung injury.

A randomized trial of the efficacy and safety of quilizumab in adults with inadequately controlled allergic asthma

Background

Quilizumab, a humanized IgG1 monoclonal antibody, targets the M1-prime segment of membrane-expressed IgE, leading to depletion of IgE-switched and memory B cells. In patients with mild asthma, quilizumab reduced serum IgE and attenuated the early and late asthmatic reaction following whole lung allergen challenge. This study evaluated the efficacy and safety of quilizumab in adults with allergic asthma, inadequately controlled despite high-dose inhaled corticosteroids (ICS) and a second controller.

Methods

Five hundred seventy-eight patients were randomized to monthly or quarterly dosing regimens of subcutaneous quilizumab or placebo for 36 weeks, with a 48-week safety follow-up. Quilizumab was evaluated for effects on the rate of asthma exacerbations, lung function, patient symptoms, serum IgE, and pharmacokinetics. Exploratory analyses were conducted on biomarker subgroups (periostin, blood eosinophils, serum IgE, and exhaled nitric oxide).

Results

Quilizumab was well tolerated and reduced serum total and allergen-specific IgE by 30–40 %, but had no impact on asthma exacerbations, lung function, or patient-reported symptom measures. At Week 36, the 300 mg monthly quilizumab group showed a 19.6 % reduction (p = 0.38) in the asthma exacerbation rate relative to placebo, but this was neither statistically nor clinically significant. Biomarker subgroups did not reveal meaningful efficacy benefits following quilizumab treatment.

Conclusions

Quilizumab had an acceptable safety profile and reduced serum IgE. However, targeting the IgE pathway via depletion of IgE-switched and memory B cells was not sufficient for a clinically meaningful benefit for adults with allergic asthma uncontrolled by standard therapy.

Trial registration

ClinicalTrials.gov NCT01582503

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0347-2) contains supplementary material, which is available to authorized users.

Histone 3.3 participates in a self-sustaining cascade of apoptosis that contributes to the progression of chronic obstructive pulmonary disease

RATIONALE

Shifts in the gene expression of nuclear protein in chronic obstructive pulmonary disease (COPD), a progressive disease that is characterized by extensive lung inflammation and apoptosis, are common; however, the extent of the elevation of the core histones, which are the major components of nuclear proteins and their consequences in COPD, has not been characterized, which is important because extracellular histones are cytotoxic to endothelial and airway epithelial cells.

OBJECTIVES

To investigate the role of extracellular histones in COPD disease progression.

METHODS

We analyzed the nuclear lung proteomes of ex-smokers with and without the disease. Further studies on the consequences of H3.3 were also performed.

MEASUREMENTS AND MAIN RESULTS

A striking finding was a COPD-specific eightfold increase of hyperacetylated histone H3.3. The hyperacetylation renders H3.3 resistant to proteasomal degradation despite ubiquitination; when combined with the reduction in proteasome activity that is known for COPD, this resistance helps account for the increased levels of H3.3. Using anti-H3 antibodies, we found H3.3 in the airway lumen, alveolar fluid, and plasma of COPD samples. H3.3 was cytotoxic to lung structural cells via a mechanism that involves the perturbation of Ca(2+) homeostasis and mitochondrial toxicity. We used the primary human airway epithelial cells and found that the antibodies to either the C or N terminus of H3 could partially reverse H3.3 toxicity.

CONCLUSIONS

Our data indicate that there is an uncontrolled positive feedback loop in which the damaged cells release acetylated H3.3, which causes more damage, adds H3.3 release, and contributes toward the disease progression.

A review of barriers to effective asthma management in Puerto Ricans: cultural, healthcare system and pharmacogenomic issues

BACKGROUND

Among the Hispanic community, Puerto Ricans have the highest prevalence of asthma and manifest the worst outcomes. The expected growth of the Hispanic population in the USA in the next several decades make elimination of disparate care in Puerto Rican asthmatics a matter of national importance. The purpose of this review of the literature (ROL) is to examine a variety of health system, genetic and cultural barriers in the Puerto Rican community which have created disparities in asthma care and outcomes among adult and pediatric Hispanic populations. In addition, this ROL describes several culturally sensitive, community-based educational interventions which can be used as a framework for future projects to improved asthma outcomes.

METHODS

Databases searched included Medline, PubMED, EBSCOhost, PsycINFO, CINAHL, Google Scholar and ERIC. Papers published in English from January 1990 to January 2012 were reviewed.

RESULTS

Health system policies, insurer compensation patterns, clinician attitudes and cultural values/folk remedies in the Puerto Rican community represent barriers to effective asthma management, the use of controller medication and the implementation of educational interventions. In addition, genetic factors involving the beta-2 adrenergic receptor gene, which impair the response to albuterol, appear to contribute to poorer outcomes in Puerto Rican asthmatics. In contrast, several comprehensive, community-based, culturally sensitive educational interventions such as Controlling Asthma in American Cities Project (CAACP), the Racial and Ethnic Approach to Community Health in the US Program and Healthy Hoops programs (REACH) have been described.

CONCLUSIONS

We believe that culturally sensitive community-based asthma education programs can serve as models for programs targeted toward Puerto Ricans to help decrease asthma morbidity. Moreover, greater sensitivity to Puerto Rican mores and folk remedies on the part of healthcare providers may improve the patient-clinician rapport and, hence, asthma outcomes. Finally, given ethnically based differences in pharmacogenomics, clinical trials targeting the Puerto Rican population may help to better define optimal asthma medication regimens in this ethnic group.

Analysis of the plasma proteome in COPD: Novel low abundance proteins reflect the severity of lung remodeling

The search for COPD biomarkers has largely employed a targeted approach that focuses on plasma proteins involved in the systemic inflammatory response and in lung injury and repair. This proof of concept study was designed to test the idea that an open, unbiased, in-depth proteomics approach could identify novel, low abundance plasma proteins i.e., ng/mL concentration, which could serve as potential biomarkers. Differentially expressed proteins were identified in a discovery group with severe COPD (FEV1 <45% predicted; n = 10). Subjects with normal lung function matched for age, sex, ethnicity and smoking history served as controls (n = 10). Pooled plasma from each group was exhaustively immunodepleted of abundant proteins, d separated by 1-D gel electrophoresis and extensively fractionated prior to LC-tandem mass spectroscopy (GeLC-MS). Thirty one differentially expressed proteins were identified in the discovery group including markers of lung defense against oxidant stress, alveolar macrophage activation, and lung tissue injury and repair. Four of the 31 proteins (i.e., GRP78, soluble CD163, IL1AP and MSPT9) were measured in a separate verification group of 80 subjects with varying COPD severity by immunoassay. All 4 were significantly altered in COPD and 2 (GRP78 and soluble CD163) correlated with both FEV1 and the extent of emphysema. In-depth, plasma proteomic analysis identified a group of novel, differentially expressed, low abundance proteins that reflect known pathogenic mechanisms and the severity of lung remodeling in COPD. These proteins may also prove useful as COPD biomarkers.

Immunodepletion plasma proteomics by tripleTOF 5600 and Orbitrap elite/LTQ-Orbitrap Velos/Q exactive mass spectrometers

Plasma proteomic experiments performed rapidly and economically using several of the latest high-resolution mass spectrometers were compared. Four quantitative hyperfractionated plasma proteomics experiments were analyzed in replicates by two AB SCIEX TripleTOF 5600 and three Thermo Scientific Orbitrap (Elite/LTQ-Orbitrap Velos/Q Exactive) instruments. Each experiment compared two iTRAQ isobaric-labeled immunodepleted plasma proteomes, provided as 30 labeled peptide fractions, and 480 LC-MS/MS runs delivered >250 GB of data in 2 months. Several analysis algorithms were compared. At 1% false discovery rate, the relative comparative findings concluded that the Thermo Scientific Q Exactive Mass Spectrometer resulted in the highest number of identified proteins and unique sequences with iTRAQ quantitation. The confidence of iTRAQ fold-change for each protein is dependent on the overall ion statistics (Mascot Protein Score) attainable by each instrument. The benchmarking also suggested how to further improve the mass spectrometry parameters and HPLC conditions. Our findings highlight the special challenges presented by the low abundance peptide ions of iTRAQ plasma proteome because the dynamic range of plasma protein abundance is uniquely high compared with cell lysates, necessitating high instrument sensitivity.

Assessment of two immunodepletion methods: off-target effects and variations in immunodepletion efficiency may confound plasma proteomics

Immunodepletion of abundant plasma proteins increases the depth of proteome penetration by mass spectrometry. However, the nature and extent of immunodepletion and the effect of off-target depletion on the quantitative comparison of the residual proteins have not been critically addressed. We performed mass spectrometry label-free quantitation to determine which proteins were immunodepleted and by how much. Two immunodepletion resins were compared: Qproteome (Qiagen) which removes albumin+immunoglobulins and Seppro IgY14+SuperMix (Sigma-Aldrich) which removes 14 target proteins plus a number of unidentified proteins. Plasma collected by P100 proteomic plasma collection tubes (BD) from 20 human subjects was individually immunodepleted to minimize potential variability, prior to pooling. The abundant proteins were quantified better when using only albumin+immunoglobulins removal (Qproteome), while lower abundance proteins were evaluated better using exhaustive immunodepletion (Seppro IgY14+SuperMix). The latter resin removed at least 155 proteins, 38% of the plasma proteome in protein number and 94% of plasma protein in mass. The depth of immunodepletion likely accounts for the effectiveness of this resin in revealing low abundance proteins. However, the more profound immunodepletion achieved with the IgY14+SuperMix may lead to false-positive fold-changes between comparison groups if the reproducibility and efficiency of the depletion of a given protein are not considered.

Respiratory epithelial cell responses to cigarette smoke: the unfolded protein response

Cigarette smoking exposes the respiratory epithelium to highly toxic, reactive oxygen nitrogen species which damage lung proteins in the endoplasmic reticulum (ER), the cell organelle in which all secreted and membrane proteins are processed. Accumulation of damaged or misfolded proteins in the ER, a condition termed ER stress, activates a complex cellular process termed the unfolded protein responses (UPR). The UPR acts to restore cellular protein homeostasis by regulating all aspects of protein metabolism including: protein translation and syntheses; protein folding; and protein degradation. However, activation of the UPR may also induce signaling pathways which induce inflammation and cell apoptosis. This review discusses the role of UPR in the respiratory epithelial cell response to cigarette smoke and the pathogenesis of lung diseases like COPD.

Heightened endoplasmic reticulum stress in the lungs of patients with chronic obstructive pulmonary disease: the role of Nrf2-regulated proteasomal activity

RATIONALE

Nuclear factor erythroid 2-related factor 2 (Nrf2), an important regulator of lung antioxidant defenses, declines in chronic obstructive pulmonary disease (COPD). However, Nrf2 also regulates the proteasome system that degrades damaged and misfolded proteins. Because accumulation of misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and ER stress-induced apoptosis, Nrf2 may potentially prevent ER stress-mediated apoptosis in COPD.

OBJECTIVES

To determine whether Nrf2-regulated proteasome function affects ER stress-mediated apoptosis in COPD.

METHODS

We assessed the expression of Nrf2, Nrf2-dependent proteasomal subunits, proteasomal activity, markers of ER stress, and apoptosis in emphysematous lungs of mice exposed to cigarette smoke (CS) as well as peripheral lung tissues from normal control subjects and patients with COPD.

MEASUREMENTS AND MAIN RESULTS

Compared with wild-type mice, emphysematous lungs of CS-exposed Nrf2-deficient mice exhibited markedly lower proteasomal activity and elevated markers of ER stress and apoptosis. Furthermore, compared with normal control subjects, lungs of patients with mild and advanced COPD showed a marked decrease in the expression of Nrf2-regulated proteasomal subunits and total proteasomal activity. However, they were associated with greater levels of ER stress and apoptosis markers. In vitro studies have demonstrated that enhancing proteasomal activity in Beas2B cells either by sulforaphane, an activator of Nrf2, or overexpression of Nrf2-regulated proteasomal subunit PSMB6, significantly inhibited cigarette smoke condensate (CSC)-induced ER stress and cell death.

CONCLUSIONS

Impaired Nrf2 signaling causes significant decline in proteasomal activity and heightens ER stress response in lungs of patients with COPD and CS-exposed mice. Accordingly, pharmacological approaches that augment Nrf2 activity may protect against COPD progression by both up-regulating antioxidant defenses and relieving ER stress.

Lymphoid follicle cells in chronic obstructive pulmonary disease overexpress the chemokine receptor CXCR3

RATIONALE

The mechanisms underlying formation of lung lymphoid follicles (LF) in chronic obstructive pulmonary disease (COPD) are unknown. The chemokine receptor CXCR3 regulates immune responses in secondary lymphoid structures elsewhere in the body and is highly expressed by Th1 lymphocytes in the airway in COPD. Because chemokine receptors control inflammatory cell homing to inflamed tissue, we reasoned that CXCR3 may contribute to LF formation in COPD.

OBJECTIVES

We assessed the expression of CXCR3 and its ligands (IP-10/CXCL10, Mig/CXCL9, and ITAC/CXCL11) by LF cells in never-smokers, smokers without COPD, and subjects with COPD.

METHODS

CXCR3, IP-10, Mig, and ITAC expression were assessed in lung sections from 46 subjects (never-smokers, smokers without COPD [S], and subjects with COPD in GOLD stages 1-4) by immunohistochemistry.

MEASUREMENTS AND MAIN RESULTS

CXCR3-expressing T cells (CD8+ or CD4+) and B cells (CD20+) were topographically distributed at the follicle periphery and center, respectively. The percentage of immunohistochemically identified CXCR3+ cells increased progressively while proceeding from S through GOLD 3-4 (P < 0.01 for GOLD 3-4 vs. S). Moreover, the number of CXCR3+ follicular cells correlated inversely with FEV(1) (r = 0.60). The CXCR3 ligands IP-10 and Mig were expressed by several cell types in and around the follicle, including CD68+ dendritic cells/ macrophages, airway epithelial cells, endothelial cells, and T and B cells.

CONCLUSIONS

These results suggest that LF form in the COPD lung by recruitment and/or retention of CXCR3-expressing T and B lymphocytes, which are attracted to the region through production of CXCR3 ligands IP-10 and Mig by lung structural and follicular cells.

Proteomic analysis of oxidative stress-responsive proteins in human pneumocytes: insight into the regulation of DJ-1 expression

Oxidative injury is believed to play an important role in the pathogenesis of lung diseases such as emphysema and lung cancer. We examined the effects of a classic reactive oxygen species, H 2O 2, on the hydrogen peroxide response proteins (HPRP) in human pneumocytes using comparative two-dimensional gel electrophoresis (2DE) and peptide mass fingerprinting. Four HPRP-associated proteins (DJ-1, peroxiredoxins [Prxs] I and IV and glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) were changed upon exposure to H 2O 2 (1 mM for 24 h). H 2O 2 exposure increased the acid (oxidized) form and decreased the basic (reduced) form of DJ-1 (pI 5.8 and 6.2, respectively), Prx I and IV and GAPDH. Mechanistic studies on DJ-1 indicated that the slow recovery of the reduced form was blocked by cyclohexamide, suggesting that the recovery was due to new protein synthesis. Total DJ-1 expression was decreased by increasing concentrations of H 2O 2. In contrast, a more complex mix of oxidants in the form of cigarette smoke extract (CSE) dose-dependently increased DJ-1 expression and produced a novel DJ-1 isoform (p I 5.6). Moreover, DJ-1 expression was higher in the lungs of chronic cigarette smokers compared with nonsmokers, a result which resembled the effects of CSE in cultured cells. These data indicate that in human pneumocytes, DJ-1 functions as an antioxidant but that no enzymatic system converts the oxidized to the reduced form. Up-regulation of DJ-1 by cigarette smoke may be a compensatory mechanism that protects the lung from oxidative stress-related injury.

Human type II pneumocyte chemotactic responses to CXCR3 activation are mediated by splice variant A

Chemokine receptors control several fundamental cellular processes in both hematopoietic and structural cells, including directed cell movement, i.e., chemotaxis, cell differentiation, and proliferation. We have previously demonstrated that CXCR3, the chemokine receptor expressed by Th1/Tc1 inflammatory cells present in the lung, is also expressed by human airway epithelial cells. In airway epithelial cells, activation of CXCR3 induces airway epithelial cell movement and proliferation, processes that underlie lung repair. The present study examined the expression and function of CXCR3 in human alveolar type II pneumocytes, whose destruction causes emphysema. CXCR3 was present in human fetal and adult type II pneumocytes as assessed by immunocytochemistry, immunohistochemistry, and Western blotting. CXCR3-A and -B splice variant mRNA was present constitutively in cultured type II cells, but levels of CXCR3-B greatly exceeded CXCR3-A mRNA. In cultured type II cells, I-TAC, IP-10, and Mig induced chemotaxis. Overexpression of CXCR3-A in the A549 pneumocyte cell line produced robust chemotactic responses to I-TAC and IP-10. In contrast, I-TAC did not induce chemotactic responses in CXCR3-B and mock-transfected cells. Finally, I-TAC increased cytosolic Ca2+ and activated the extracellular signal-regulated kinase, p38, and phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B kinases only in CXCR3-A-transfected cells. These data indicate that the CXCR3 receptor is expressed by human type II pneumocytes, and the CXCR3-A splice variant mediates chemotactic responses possibly through Ca2+ activation of both mitogen-activated protein kinase and PI 3-kinase signaling pathways. Expression of CXCR3 in alveolar epithelial cells may be important in pneumocyte repair from injury.

Cigarette smoke induces an unfolded protein response in the human lung: a proteomic approach

Cigarette smoking, which exposes the lung to high concentrations of reactive oxidant species (ROS) is the major risk factor for chronic obstructive pulmonary disease (COPD). Recent studies indicate that ROS interfere with protein folding in the endoplasmic reticulum and elicit a compensatory response termed the "unfolded protein response" (UPR). The importance of the UPR lies in its ability to alter expression of a variety of genes involved in antioxidant defense, inflammation, energy metabolism, protein synthesis, apoptosis, and cell cycle regulation. The present study used comparative proteomic technology to test the hypothesis that chronic cigarette smoking induces a UPR in the human lung. Studies were performed on lung tissue samples obtained from three groups of human subjects: nonsmokers, chronic cigarette smokers, and ex-smokers. Proteomes of lung samples from chronic cigarette smokers demonstrated 26 differentially expressed proteins (20 were up-regulated, 5 were down-regulated, and 1 was detected only in the smoking group) compared with nonsmokers. Several UPR proteins were up-regulated in smokers compared with nonsmokers and ex-smokers, including the chaperones, glucose-regulated protein 78 (GRP78) and calreticulin; a foldase, protein disulfide isomerase (PDI); and enzymes involved in antioxidant defense. In cultured human airway epithelial cells, GRP78 and the UPR-regulated basic leucine zipper, transcription factors, ATF4 and Nrf2, which enhance expression of important anti-oxidant genes, increased rapidly (< 24 h) with cigarette smoke extract. These data indicate that cigarette smoke induces a UPR response in the human lung that is rapid in onset, concentration dependent, and at least partially reversible with smoking cessation. We speculate that activation of a UPR by cigarette smoke may protect the lung from oxidant injury and the development of COPD.

Inhibition by salmeterol and cilomilast of fluticasone-enhanced IP-10 release in airway epithelial cells

The CXC chemokines, IP-10/CXCL10 and IL-8/CXCL8, play a role in obstructive lung disease by attracting Th1/Tc1 lymphocytes and neutrophils, respectively. Inhaled corticosteroids (ICS) and long acting beta 2-agonists (LABA) are widely used. However, their effect(s) on the release of IP-10 and IL-8 by airway epithelial cells are poorly understood. This study examined the effects of fluticasone, salmeterol, and agents which raise intracellular cAMP (cilomilast and db-cAMP) on the expression of IP-10 and IL-8 protein and mRNA. Studies were performed in cultured human airway epithelial cells during cytokine-stimulated IP-10 and IL-8 release. Cytokine treatment (TNF-alpha, IL-1beta and IFN-gamma) increased IP-10 and IL-8 protein and mRNA levels. Fluticasone (0.1 nM to 1 microM) increased IP-10 but reduced IL-8 protein release without changing IP-10 mRNA levels assessed by real time RT-PCR. The combination of salmeterol (1 micro M) and cilomilast (1-10 mu M) reduced IP-10 but had no effect on IL-8 protein. Salmeterol alone (1 micro M) and db-cAMP alone (1 mM) antagonised the effects of fluticasone on IP-10 but not IL-8 protein. In human airway epithelial cells, inhibition by salmeterol of fluticasone-enhanced IP-10 release may be an important therapeutic effect of the LABA/ICS combination not present when the two drugs are used separately.

CXCR3 chemokine receptor-induced chemotaxis in human airway epithelial cells: role of p38 MAPK and PI3K signaling pathways

Human airway epithelial cells (HAEC) constitutively express the CXC chemokine receptor CXCR3, which regulates epithelial cell movement. In diseases such as chronic obstructive pulmonary disease and asthma, characterized by denudation of the epithelial lining, epithelial cell migration may contribute to airway repair and reconstitution. This study compared the potency and efficacy of three CXCR3 ligands, I-TAC/CXCL11, IP-10/CXCL10, and Mig/CXCL9, as inducers of chemotaxis in HAEC and examined the underlying signaling pathways involved. Studies were performed in cultured HAEC from normal subjects and the 16-HBE cell line. In normal HAEC, the efficacy of I-TAC-induced chemotaxis was 349 +/- 88% (mean +/- SE) of the medium control and approximately one-half the response to epidermal growth factor, a highly potent chemoattractant. In normal HAEC, Mig, IP-10, and I-TAC induced chemotaxis with similar potency and a rank order of efficacy of I-TAC = IP-10 > Mig. Preincubation with pertussis toxin completely blocked CXCR3-induced migration. Of interest, intracellular [Ca(2+)] did not rise in response to I-TAC, IP-10, or Mig. I-TAC induced a rapid phosphorylation (5-10 min) of two of the three MAPKs, i.e., p38 and ERK1/2. Pretreatment of HAEC with the p38 inhibitor SB 20358 or the PI3K inhibitor wortmannin dose-dependently inhibited the chemotactic response to I-TAC. In contrast, the ERK1/2 inhibitor U0126 had no effect on chemotaxis. These data indicate that in HAEC, CXCR3-mediated chemotaxis involves a G protein, which activates both the p38 MAPK and PI3K pathways in a calcium-independent fashion.

CXCR3 surface expression in human airway epithelial cells: cell cycle dependence and effect on cell proliferation

We recently demonstrated that human bronchial epithelial cells (HBEC) constitutively express the CXC chemokine receptor CXCR3, which when activated, induces directed cell migration. The present study in HBEC examined the relative expression of the CXCR3 splice variants CXCR3-A and -B, cell cycle dependence of CXCR3 expression, and the effects of the CXCR3 ligand, the interferon-gamma-inducible CXC chemokine I-TAC/CXCL11, on DNA synthesis and cell proliferation. Both CXCR3-A and -B mRNA, assessed by real-time RT-PCR, were expressed in normal HBEC (NHBEC) and the HBEC line 16-HBE. However, CXCR3-B mRNA was 39- and 6-fold greater than CXCR3-A mRNA in NHBEC and 16-HBE, respectively. Although most HBEC (>80%) assessed by flow cytometry and immunofluorescence microscopy contained intracellular CXCR3, only a minority (<40%) expressed it on the cell surface. In this latter subset of cells, most (>75%) were in the S + G(2)/M phases of the cell cycle. Stimulation of CXCR3 with I-TAC enhanced thymidine incorporation and cell proliferation and increased p38 and ERK1/2 phosphorylation. These data indicate that 1) human airway epithelial cells primarily express CXCR3-B mRNA, 2) surface expression of CXCR3 is largely confined to the S + G(2)/M phases of the cell cycle, and 3) activation of CXCR3 induces DNA synthesis, cell proliferation, and activation of MAPK pathways. We speculate that activation of CXCR3 exerts a mitogenic effect in HBEC, which may be important during airway mucosal injury in obstructive airway diseases such as asthma and chronic obstructive pulmonary disease.

Regulation of interleukin-1beta and interleukin-1beta inhibitor release by human airway epithelial cells

In asthma, human airway epithelial cells (HAECs) regulate the intensity of mucosal inflammation, in part, by releasing the pro-inflammatory cytokine interleukin (IL)-1beta. However, the IL-1beta inhibitors, IL-1 receptor antagonist (IL-1RA) and soluble IL-1 receptor type II (sIL-1RII), regulate IL-1beta bioactivity. In order to better understand the control of IL-1beta activity in the airway mucosa, the role(s) of tumour necrosis factor (TNF)-alpha, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in the release of IL-1beta and its inhibitors by cultured HAECs were examined. HAECs were treated with TNF-alpha (2-200 ng.mL(-1)), dibutyryl cAMP (0.01-1 mM), 8-bromo-cGMP (0.01-1 mM) or vehicle for 24 h, and cytokine levels in the HAEC-conditioned medium were measured by enzyme-linked immunosorbent assay. HAECs produced IL-1beta, IL-1RA and sIL-1RII constitutively, but the inhibitor concentrations greatly exceeded that of IL-1beta (by approximately 100- and approximately 550-fold, respectively). TNF-alpha dose-dependently increased the levels of all IL-1beta cytokine family members. However, over the range of TNF-alpha concentrations studied, IL-1beta concentration increased more than those of its inhibitors. cAMP increased constitutive and TNF-alpha-stimulated IL-1beta release but reduced that of sIL-1RII. In contrast, cGMP had no effect on IL-1beta but reduced IL-1RA and sIL-1RII release. Under basal conditions, the disproportionate release of inhibitors relative to interleukin-1beta by human airway epithelial cells probably prevents interleukin-1beta-mediated biological effects. Tumour necrosis factor-alpha, cyclic adenosine monophosphate and cyclic guanosine monophosphate may potentiate mucosal inflammation by increasing interleukin-1beta levels relative to those of its inhibitors in the airway mucosa.

The chemokine receptor CXCR3 and its splice variant are expressed in human airway epithelial cells

Activation of the chemokine receptor CXCR3 by its cognate ligands induces several differentiated cellular responses important to the growth and migration of a variety of hematopoietic and structural cells. In the human respiratory tract, human airway epithelial cells (HAEC) release the CXCR3 ligands Mig/CXCL9, IP-10/CXCL10, and I-TAC/CXCL11. Simultaneous expression of CXCR3 by HAEC would have important implications for the processes of airway inflammation and repair. Accordingly, in the present study we sought to determine whether HAEC also express the classic CXCR3 chemokine receptor CXCR3-A and its splice variant CXCR3-B and hence may respond in autocrine fashion to its ligands. We found that cultured HAEC (16-HBE and tracheocytes) constitutively expressed CXCR3 mRNA and protein. CXCR3 mRNA levels assessed by expression array were approximately 35% of beta-actin expression. In contrast, CCR3, CCR4, CCR5, CCR8, and CX3CR1 were <5% beta-actin. Both CXCR3-A and -B were expressed. Furthermore, tracheocytes freshly harvested by bronchoscopy stained positively for CXCR3 by immunofluorescence microscopy, and 68% of cytokeratin-positive tracheocytes (i.e., the epithelial cell population) were positive for CXCR3 by flow cytometry. In 16-HBE cells, CXCR3 receptor density was approximately 78,000 receptors/cell when assessed by competitive displacement of 125I-labeled IP-10/CXCL10. Finally, CXCR3 ligands induced chemotactic responses and actin reorganization in 16-HBE cells. These findings indicate constitutive expression by HAEC of a functional CXC chemokine receptor, CXCR3. Our data suggest the possibility that autocrine activation of CXCR3 expressed by HAEC may contribute to airway inflammation and remodeling in obstructive lung disease by regulating HAEC migration.

Glucocorticoid effects on the beta-adrenergic receptor-adenylyl cyclase system of human airway epithelium

BACKGROUND

Activation of the beta(2)-adrenergic receptor (beta(2)AR) system expressed by human airway epithelial cells elicits a variety of cyclic adenosine monophosphate (cAMP)-dependent processes that help determine airway caliber and the intensity of airway inflammation in asthma. Glucocorticoids, mainstays in the treatment of asthma, profoundly affect the expression and function of the beta(2)-adrenergic receptor-adenylyl cyclase (beta(2)AR-AC) system in a variety of cell types. However, the effects of glucocorticoids on the beta(2)AR-AC system expressed by human airway epithelial cells are unstudied.

OBJECTIVE

We examined the effects of dexamethasone (DEX) on beta(2)AR gene expression and the function of the beta(2)AR-AC system in cultured human airway epithelial cells.

METHODS

Studies were performed in normal airway epithelial cells and BEAS-2B cells. Beta(2)AR gene expression was assessed from measurements of beta-adrenergic receptor density, beta(2)AR mRNA, and the activity of a full-length beta(2)AR promoter-luciferase reporter construct. The function of the beta(2)AR-AC system was assessed from cAMP production in response to the beta(2)-agonist isoproterenol and the expression of the stimulatory G protein G(alpha)s.

RESULTS

DEX had no effect on beta-adrenergic receptor density or on the beta(1)/beta(2) ratio over a wide range of concentrations and exposure times. However, DEX significantly but transiently enhanced beta(2)AR mRNA levels (approximately 1.5-fold) and beta(2)AR promoter activity (approximately 1.5-fold), indicating increased beta(2)AR gene transcription. DEX also dose-dependently enhanced cAMP responses to isoproterenol but not to forskolin, a direct activator of adenylyl cyclase. DEX-induced changes in cAMP production were associated with small (approximately 15%) increases in G(alpha)s expression.

CONCLUSIONS

These data indicate that glucocorticoids only transiently enhance beta(2)AR gene transcription and fail to increase steady-state levels of beta(2)AR protein in human airway epithelial cells. Nonetheless, glucocorticoid-induced effects on the beta(2)AR-AC system of human airway epithelial cells contribute to the beneficial effects of corticosteroids in asthma by enhancing the functional response to beta(2)-agonists.

Nuclear factor-kappa B augments beta(2)-adrenergic receptor expression in human airway epithelial cells

Interleukin (IL)-1 beta increases beta(2)-adrenergic receptor (beta(2)-AR) mRNA and density by protein kinase C (PKC)-dependent mechanisms in human airway epithelial cells. The present study examined the role of several nuclear transcription factors in the PKC-activated upregulation of beta(2)-AR expression. BEAS-2B cells were exposed to the PKC activator phorbol 12-myristate 13-acetate (PMA; 0.1 microM for 2-18 h). PMA had no effect on activator protein (AP)-2 or cAMP response element binding protein DNA binding activity but markedly increased nuclear factor (NF)-kappa B and AP-1 binding as assessed by electrophoretic gel mobility shift assay. PMA also increased the activity of a beta(2)-AR promoter-luciferase reporter construct in transiently transfected cells. These effects were inhibited by the PKC inhibitors Ro-31-8220 and calphostin C. Furthermore, with increasing Ro-31-8220, beta(2)-AR promoter-reporter activity correlated closely with both NF-kappa B and AP-1 activities (r > 0.89 for both). Finally, the selective NF-kappa B inhibitor MG-132 dose dependently reduced NF-kappa B binding and beta(2)-AR promoter activity but increased AP-1 binding. We conclude that PKC-induced upregulation of beta(2)-AR expression in human airway epithelial cells appears to be mediated, at least in part, by increases in NF-kappa B activity.

IL-1beta enhances beta2-adrenergic receptor expression in human airway epithelial cells by activating PKC

Protein kinase C (PKC)-activated signal transduction pathways regulate cell growth and differentiation in many cell types. We have observed that interleukin (IL)-1beta upregulates beta2-adrenergic receptor (beta2-AR) density and beta2-AR mRNA in human airway epithelial cells (e.g., BEAS-2B). We therefore tested the hypothesis that PKC-activated pathways mediate IL-1beta-induced beta-AR upregulation. The role of PKC was assessed from the effects of 1) the PKC activator phorbol 12-myristate 13-acetate (PMA) on beta-AR density, 2) selective PKC inhibitors (calphostin C and Ro-31-8220) on beta-AR density, and 3) IL-1beta treatment on the cellular distribution of PKC isozymes. Recombinant human IL-1beta (0.2 nM for 18 h) increased beta-AR density to 213% of control values (P < 0.001). PMA (1 microM for 18 h) increased beta-AR density to 225% of control values (P < 0.005), whereas Ro-31-8220 and calphostin C inhibited the IL-1beta-induced upregulation of beta-AR in dose-dependent fashion. PKC isozymes detected by Western blotting included alpha, betaII, epsilon, mu, zeta, and lambda/iota. IL-1beta increased PKC-mu immunoreactivity in the membrane fraction and had no effect on the distribution of the other PKC isozymes identified. These data indicate that IL-1beta-induced beta-AR upregulation is mimicked by PKC activators and blocked by PKC inhibitors and appears to involve selective activation of the PKC-mu isozyme. We conclude that signal transduction pathways activated by PKC-mu upregulate beta2-AR expression in human airway epithelial cells.

Chronic effects of inhaled albuterol on beta-adrenoceptor system function in human respiratory cells

The in vivo effects of beta-adrenergic receptor (betaAR) agonists given chronically by metered-dose inhaler (MDI) on the molecular components of the beta-adrenoceptor system expressed by human respiratory cells are poorly understood. This study examined the effects of inhaled albuterol (180 microg four times daily for 7 days) on betaAR function of airway epithelial cells (AECs) and alveolar macrophages (AMs) freshly isolated from 10 normal subjects. Responses were related to beta2AR genotype in codons 16 and 27, regions which affect chronic responses to beta2-agonists. In AEC, betaAR density and adenosine cyclic 3',5'-phosphate (cAMP) production in response to isoproterenol (ISO) were significantly lower in the albuterol versus placebo treatment arm (p < 0.01 for both). Moreover, in AEC, albuterol treatment increased betaAR-kinase (betaARK) protein immunoreactivity. In contrast, in AM, albuterol tended to decrease betaAR density and cAMP production but changes did not achieve statistical significance (p > 0.20 for both) and had no effect on betaARK immunoreactivity. Changes in betaAR density occurred in all subjects but tended to be greater in subjects with the glycine 16 genotype. In cultured cells exposed to equal concentrations of beta-agonist in vitro, the magnitude of betaAR down-regulation (p < 0.05) and cAMP densensitization (p < 0.05) was greater in AEC than AM. These results indicate that albuterol taken by inhalation in a therapeutically relevant dose for 1 week produces betaAR down-regulation, densensitizes the cAMP response of airway epithelial cells to a beta2-adrenergic agonist, and increases betaARK immunoreactivity. Greater densensitization of AEC than AM in response to chronic albuterol inhalation likely reflects cell type-specific responses.

Salmeterol added to inhaled corticosteroid therapy is superior to doubling the dose of inhaled corticosteroids: a randomized clinical trial

This randomized, double-blind, double-dummy, parallel group clinical trial compared the efficacy and safety of adding salmeterol xinafoate to concurrent inhaled beclomethasone dipropionate therapy with doubling the dose of beclomethasone dipropionate in patients experiencing symptoms on low-dose beclomethasone. Salmeterol added to low-dose beclomethasone was superior (p < or = 0.05) to doubling the dose of beclomethasone in improving peak expiratory flow (PEF) and forced expiratory volume in 1 sec (FEV1), and in reducing symptoms of asthma, sleep loss, nighttime awakenings, and use of albuterol. Both treatment regimens had comparable safety profiles. In asthma patients inadequately controlled despite the use of low-dose inhaled corticosteroids (i.e., less than 400 microg per day), the addition of salmeterol may be a more effective treatment option than doubling the dose of inhaled corticosteroids.

Variability of electrophrenic diaphragm twitch stimulation over time in normal subjects

Transcutaneous electrophrenic twitch stimulation is a potentially powerful way to assess diaphragm contractile function in response to interventions which may alter respiratory muscle strength and endurance. At present, the variability of the transdiaphragmatic twitch pressure (Pdi(T)) over a several hour period is not well described. The present study examines the reproducibility of Pdi(T) amplitude and the twitch occlusion technique of assessing maximum transdiaphragmatic pressure (Pdi(max)) in seven normal adults stimulated intermittently every hour for a total 4-h period. In one subject, data were obtained on two occasions separated by a 2-month interval. Among all subjects, the Pdi(T) amplitude expressed as a percentage of the Pdi(max) was highly reproducible over 4 h (coefficient of variation 5.3). Peak Pdi(T) was inversely related to graded voluntary Pdi (r = -0.0996) and the relationship was virtually identical over 4 h (r = - 0.999, P = 0.96). These data show that Pdi(T) at functional residual capacity and the twitch occlusion relationship are highly reproducible.

Dose-response characteristics of nebulized albuterol in the treatment of acutely ill, hospitalized asthmatics

We investigated the bronchodilator dose-response to nebulized albuterol and the dose of albuterol which produces maximal bronchodilation in the acutely ill, hospitalized asthmatic. Consecutively admitted patients from the emergency room in status asthmaticus who fulfilled the inclusion criteria (age <41 years old and <12 pack-years of smoking) were studied. Albuterol was administered by nebulizer (Puritan-Bennett Raindrop) in repeated 2.5-mg treatments up to a total dose of 10 mg and the bronchodilator response was measured by a computerized spirometer. Twenty-two patients were studied. Baseline spirometry showed a (mean +/- SE) forced expiratory volume in 1 sec (FEV1) of 1.26 +/- 0.14 L (42 +/- 4.0% predicted), which increased significantly (p < 0.05) during albuterol titration to a maximum FEV1 of 1.70 +/- 0.19 L (57 +/- 5% of predicted). After cumulative doses of 2.5, 5.0, 7.5, and 10.0 mg of nebulized albuterol, 27%, 45%, 72%, and 77% of patients, respectively, attained maximum bronchodilation. The remaining 23% of patients did not respond to doses up to 10 mg of albuterol. The maximum FEV1 response to albuterol did not correlate with the initial severity of airflow obstruction (r = 0.36, p > 0.05). Pulse rate and arterial oxygen saturation were not significantly affected by nebulized albuterol up to a total dose of 10 mg. No arrhythmias were noted. In summary, most hospitalized asthmatics (72%) required a cumulative dose of 7.5 mg of nebulized albuterol to achieve maximum bronchodilation and a large fraction (50%) required higher albuterol doses than the standard 2.5 mg. The bronchodilatory response to nebulized albuterol varied widely among patients in status asthmaticus and could not be predicted from the initial severity of airflow obstruction. Because side effects were minimal, it would be reasonable to use 7.5 mg of nebulized albuterol as initial therapy. Alternatively, dose-response titration with albuterol would be advantageous.

Effects of topical corticosteroids on inflammatory mediator-induced eicosanoid release by human airway epithelial cells

BACKGROUND

Airway epithelial cells are among the first cells to come in contact with aerosolized corticosteroids. However, the relative potencies and time course of action of the several commonly used aerosolized corticosteroids on eicosanoid production by airway epithelial cells are unknown.

OBJECTIVES

This study compared the effects of fluticasone, budesonide, and triamcinolone on eicosanoid output by human airway epithelial cells in vitro. We also determined the spectrum of eicosanoids affected and the mechanism for corticosteroid action.

METHODS

Cultured BEAS-2B airway epithelial cells (a transformed cell line) were exposed to corticosteroids (1 nmol/L to 1 micromol/L) for 2 to 48 hours and then assayed for basal- and bradykinin (BK)-stimulated eicosanoid output. The eicosanoid profile was identified by HPLC in tritiated arachidonic acid prelabelled cells, and PGE2, the major eicosanoid product, was quantitated by RIA. The effect of corticosteroids on the immunoreactivity of key proteins involved in eicosanoid metabolism (ie, cyclooxygenase [COX], phospholipase A2 [PLA2], and Clara cell protein, a PLA2 inhibitor) was determined by Western blotting.

RESULTS

Eicosanoid output was largely confined to prostaglandins with values of 5 +/- 2 and 82 +/- 35 ng PGE2/10(6) cells for basal- and BK stimulation, respectively (n = 8). All 3 corticosteroids inhibited basal- and BK-induced PGE2 output in a dose- and time-dependent manner. Fluticasone and budesonide completely eliminated PGE2 output in nanomolar concentrations in contrast to triamcinolone, which required micromolar concentration. The rank order of potency was: fluticasone = budesonide > triamcinolone. The time course of action for PGE2 inhibition also differed, with budesonide acting more slowly than the other 2 corticosteroids (P = .04). All 3 corticosteroids markedly reduced COX2 with little effect on COX1, cPLA2 (Type IV), or iPLA2 (Type VI) immunoreactivity or their relative distribution in cytosol versus membrane fractions. Clara cell protein immunoreactivity was undetectable in control and corticosteroid-treated cell lysates.

CONCLUSION

These results show that in a human airway epithelial cell line, the 3 inhaled corticosteroids commonly used to treat asthma differ in onsets of action as inhibitors of prostaglandin synthesis and vary considerably in potency. All 3 corticosteroids act mechanistically in similar fashion by inhibiting COX2 synthesis.

IL-1 beta alters beta-adrenergic receptor adenylyl cyclase system function in human airway epithelial cells

Inflammatory cells release a variety of cytokines, including interleukin (IL)-1 beta, into the airway in asthma. This study examined the effects of human IL-1 beta on the function of the beta-adrenergic receptor (beta AR)-adenylyl cyclase (AC) system in BEAS-2B cells, a human airway epithelial cell line. IL-1 beta markedly increased beta AR density (Bmax; P < 0.001) primarily by increasing the percentage of the beta 2AR subtype (from 67 to 91%; P < 0.001). Bmax increased monotonically over time in response to 200 pM IL-1 beta and was approximately 2.5-fold greater than control cells between 36 and 42 h. In contrast, the concentration response of Bmax to IL-1 beta given for 18 h was biphasic. Bmax increased with IL-1 beta concentrations from 2 to 200 pM, but, at > 200 pM, it decreased progressively toward control values. IL-1 beta-induced increases in Bmax with IL-1 beta were associated with approximately threefold increases in beta 2 AR mRNA and were blocked by the protein synthesis inhibitor cycloheximide. Despite the marked increase in Bmax, however, IL-1 beta depressed adenosine 3',5'-cyclic monophosphate (cAMP) responses to isoproterenol and forskolin, a direct activator of AC (P < 0.001 by analysis of variance for both). The inhibitory effect of IL-1 beta on cAMP production appeared to be explained by increases in the activity of an inhibitory GTP binding protein because IL-1 beta treatment increased the activity of a pertussis toxin ADP-ribosylated Gi alpha protein by approximately 2.5-fold; and pretreatment of intact cells with pertussis toxin inhibited the effect of IL-1 beta on cAMP production. These data indicate that IL-1 beta-mediated changes in the beta AR-AC system function in airway epithelial cells are complex and involve expression of receptor protein, GTP binding protein, and possibly AC itself. Increases in IL-1 beta may contribute to abnormalities in airway function in subjects with asthma.

Chronic effects of catecholamines on the beta 2-adrenoreceptor system in cultured human airway epithelial cells

Chronic catecholamine treatment induces beta-adrenergic receptor (beta AR) downregulation, i.e., a loss of total cell receptors. In the human respiratory tract, the mechanism(s) underlying beta AR downregulation remains poorly understood. The present study, therefore, examined the effects of 24 h of exposure to isoproterenol (Iso; 10 nM or 1 microM) on beta AR density and the rate of beta AR degradation, steady-state beta 2-adrenergic receptor (beta 2 AR) mRNA levels, and the content of Gs alpha and Gi alpha proteins in cultured human bronchial epithelial cells (i.e., the BEAS-2B cell line). beta AR density assessed by binding with [125I]iodopindolol decreased in a dose-dependent fashion with 24 h of Iso exposure. With Iso (1 microM), beta AR density decreased by approximately 82%. In contrast, forskolin (100 microM) and dibutyryl adenosine 3',5'-cyclic monophosphate (1 mM), agents that also increase adenosine 3',5'-cyclic monophosphate (cAMP) levels, had no significant effect on beta AR density. Iso exposure also elicited a concomitant decrease in Iso-stimulated cAMP but had no significant effect on the content of the G proteins G alpha i2 and Gs alpha assessed by immunoblotting and toxin-catalyzed ADP ribosylation. Of note, Iso exposure (1 microM) had no effect on steady-state levels of beta 2 AR mRNA measured both by Northern analysis and by reverse transcriptase-polymerase chain reaction. However, beta AR half-life assessed in the presence of the protein synthesis inhibitor cycloheximide was reduced by approximately 60% in Iso-treated cells (i.e., from 37 h in control to 16 h in 1 microM Iso). These results suggest that, in human airway epithelial cells, beta 2 AR downregulation 1) is not primarily driven by intracellular cAMP levels, 2) is not associated with significant decreases in steady-state levels of beta 2 AR mRNA, and 3) is largely posttranslationally regulated by increases in the rate of receptor protein degradation.

Effect of lung volume on the respiratory action of the canine sternomastoid

We tested the hypothesis that because the resting length of the canine sternomastoid (SM) muscles is relatively insensitive to lung volume change, the SM may maintain its inspiratory force generation regardless of lung volume. The relationships between SM pre- and postcontraction in situ fiber lengths and SM-produced inspiratory pressure generation [i.e., esophageal (Pes)] and rib cage displacements were examined in adult supine anesthetized dogs at residual volume (RV), functional residual capacity, and total lung capacity. SM muscle contraction was produced by isolated bilateral supramaximal electrical stimulation during hyperventilation-induced apnea. In all animals, SM contraction produced negative change in Pes (i.e., an inspiratory action). Passively increasing lung volume from RV to total lung capacity decreased (P < or = 0.01) the SM-produced Pes by -66 +/- 4% but had a relatively small effect on SM in situ pre- and postcontraction fiber length (< 3%). Whereas SM contraction at RV produced a cranial displacement of the sternum and increased the upper rib cage cross-sectional area, passively elevating lung volume diminished the SM-produced expansion of the upper rib cage. Hyperinflation did not increase the impedance of the sternum to cranial displacement during SM contraction, suggesting that hyperinflation caused a dissociation between the mechanical action of the sternum and the upper rib cage. These results suggest that mechanical dissociation of the ribs and sternum may diminish the contribution of the SM to inspiratory volume generation when breathing is done from elevated end-expiratory lung volumes.

Expression and function of the beta-adrenergic receptor coupled-adenylyl cyclase system on human airway epithelial cells

Beta-adrenergic agonist-mediated activation of the beta receptor coupled-adenylyl cyclase (beta AR-AC) system expressed by human airway epithelial cells alters airway function. However, little is known about the magnitude of expression, subtype, and function of the beta receptor-adenylyl cyclase (beta AR-AC) system in human airway epithelial cells from healthy, nonsmoking subjects. Therefore, we characterized beta AR number and subtype and the cAMP response to isoproterenol (iso) in acutely dissociated human tracheocytes harvested from 22 healthy, nonsmoking adults during fibroptic bronchoscopy. Moreover, because the regulation of beta AR-AC system function in response to beta-agonists or inflammatory mediators released into the airway in asthma is poorly understood, we examined the cAMP response to iso after 30 min exposure of cells to iso or the protein kinase C activator, sn-1,2-dioctanoyl glycerol (diC8). The beta AR-AC system was highly expressed and functional in human airway epithelial cells. Group mean beta AR density (i.e., Bmax), equilibrium dissociation constant (Kd), and the percentage of beta 2AR subtypes assessed by radioligand binding were approximately 8,900 receptors/cell, 45 pM, and approximately 80%, respectively. Mean maximum cAMP production was approximately 42 pmol/10(5) cells, and the mean EC50 of the response to iso was 131 nM. However, Bmax and cAMP responses to iso varied considerably across subjects. For example, Bmax varied ninefold, and the EC50 of the cAMP response varied 39-fold interindividually. The EC50 was inversely related to beta AR density (r = -0.81, p < 0.05), suggesting that sensitivity of the cAMP response to iso was in part dependent on beta AR density. In all experiments, cAMP responses to iso stimulation were markedly desensitized in dose-dependent fashion by 30 min pretreatment with iso or diC8. For example, pretreatment with iso 10 microM or diC8 100 microM reduced maximum cAMP production to 22 and 63% of control values, respectively. These data indicate that: (1) the beta AR-AC system is highly expressed on acutely dissociated airway epithelial cells from normal adult, but beta AR expression and its functional coupling to adenylyl cyclase vary considerably interindividually; and (2) the beta AR-AC system of normal human airway epithelial cells is rapidly desensitized by exposure to beta-adrenergic agonists or activators of PKC.

Eicosanoid production in rabbit tracheal epithelium by adenine nucleotides: mediation by P2-purinoceptors

Adenosine triphosphate (ATP) acting through epithelial nucleotide receptors exerts multiple physiologic actions on airway mucociliary clearance and caliber. However, the effect of ATP on arachidonate metabolism in the airway remains unknown. In this study, the ability of ATP to regulate eicosanoid production was studied in vitro in full-thickness rabbit tracheal strips and separately in rabbit epithelial explant cultures. In the freshly isolated strips, ATP increased prostaglandin E2 (PGE2) release in a dose-dependent fashion, with an activation threshold at 10 microM ATP and a 3.5-fold increase in PGE2 output at 1 mM ATP. Epithelium removal decreased 1 mM ATP-evoked PGE2 release by 68%. Reverse-phase, high-pressure liquid chromatography (HPLC) of media from 3H-arachidonic acid-incubated epithelial explants exposed to 1 mM ATP demonstrated increased output of the cyclooxygenase products PGE2 and prostaglandin F2a (PGF2a). Other identifiable eicosanoids did not increase. The concentration-response for ATP-induced PGE2 release by explants was similar to that of tracheal strips. PGE2 release by 1 mM ATP was 27% of that elicited by ionomycin (10 microM) and was markedly inhibited by indomethacin (10 microM). Purinoceptor agonist-stimulated PGE2 release by the epithelium yielded a rank order of potency of uridine triphosphate (UTP) > or = ATP > 2-methylthio-ATP (2MeSATP) >> alpha,beta-methyleneadenosine-5'-triphosphate (AMP-CPP) > or = adenosine. These results indicate that ATP, acting primarily through an epithelial P2-purinoceptor similar to the P2a subtype, stimulates eicosanoid metabolism in rabbit airway epithelium via the cyclooxygenase pathway, producing PGE2 as the predominant species.

Acute and Chronic Effects of Misoprostol in the Control of Asthma: A Pilot Study in Five Subjects

Asthma is an inflammatory disease involving the airways. E-series prostaglandins have potent anti-inflammatory effects on neutrophils and T lymphocytes. Accordingly, we tested the acute (i.e., 6 h) and chronic (i.e., 1 week) effects of oral misoprostol 200 &mgr;g in five stable asthmatics. A double-blind, randomized, crossover design was used. Airway function was assessed from measurements of forced expiratory volume in 1 s (FEV(1)). The number of puffs of the inhaled beta-adrenergic agonist bronchodilator, albuterol, taken for symptomatic rescue, was assessed by diary. FEV(1) measured serially for 6 h after 200 &mgr;g misoprostol was similar on misoprostol and placebo days in all subjects. In contrast, three of the five subjects showed appreciable increases in FEV(1) during a week of misoprostol compared to either baseline or placebo week. Two subjects showed no change in the FEV(1) with 1 week of misoprostol. All three of the subjects who kept a diary decreased the number of puffs of albuterol during the misoprostol compared to placebo period. Of note, in these three subjects, airway function improved (n = 1) or remained the same (n = 2) despite a diminution in the number of puffs of a beta-agonist administered. None of the subjects administered the 200-&mgr;g oral dose QID reported any significant symptoms or adverse reaction. In conclusion, several inferences can be drawn from this early preliminary study. These data suggest that a trial involving a large number of subjects, a longer period of treatment, and a more objective method of assessing inhaler use may be useful in evaluating the chronic effects of misoprostol in asthma.

Comparison of diaphragm strength between healthy adult elderly and young men

To test the hypothesis that aging is associated with a reduction in the diaphragm's force-generating capacity, we compared the maximum transdiaphragmatic pressure (Pdimax) obtained during voluntary maximal inspiratory efforts in nine young (19-28 yr) and ten elderly (65-75 yr) subjects. The relationship between Pdi and lung volume was compared in the two groups by having subjects make maximal inspiratory maneuvers at specified lung volumes (i.e., 20, 40, and 80% vital capacity). Subjects underwent symptom-limited exercise tests to characterize their aerobic capacities and evaluate the relationship between aerobic capacity and Pdimax. The average Pdimax of the elderly subjects (128 +/- 9 cm H2O) was significantly lower (p < 0.003) than the average Pdimax of the younger subjects (171 +/- 8 cm H2O). In the elderly, Pdi was lower across the range of lung volumes tested (p < 0.001), and Pdimax occurred at similar relative lung volumes (elderly, at 47% total lung capacity [TLC]; young, at 50% TLC) in both groups. The elderly subjects were quite fit based on their VO2max, and there was no significant relationship between Pdimax and VO2max. This study suggests that diaphragm strength is reduced in elderly individuals. This age-related decrease in diaphragm strength may predispose elderly patients to diaphragm fatigue in the presence of conditions that impair inspiratory muscle function or increase ventilatory load.

Dilatory effects of upper airway muscle contraction induced by electrical stimulation in awake humans

During sleep, diminished activity of upper airway dilator muscles (UADMs) is believed to increase upper airway (UAW) resistance and ultimately cause collapse of the UAW. In anesthetized dogs, electrically induced UADM contraction reduces UAW resistance and collapsibility. In this study, we measured the effects of electrically induced contraction of UADMs on pharyngeal resistance (Rph) in seven awake healthy subjects. UAW partial occlusion was achieved by applying external pressure to the submental hyoid region, leading to increased Rph. Transmucosal electrical stimulation (ES) of the base of the tongue was used to preferentially stimulate the genioglossus muscle. Transcutaneous ES using submental and paralaryngeal electrodes were used to preferentially stimulate the geniohyoid and the sternohyoid and sternothyroid muscles, respectively. During the unobstructed state, Rph averaged 6.11 +/- 0.48 cmH2O.l-1.s, and ES produced minimal resistance changes for all stimulation sites tested. In contrast, during the application of external pressure, when Rph was raised to an average of 190 +/- 14% of the baseline value, sublingual ES reduced resistance from 11.67 +/- 1.90 to 6.77 +/- 1.30 cmH2O.l-1.s (P < 0.01). ES at the other sites during the raised Rph state produced only minor statistically insignificant changes in Rph, even when combined submental and paralaryngeal ES was applied. Likewise, only sublingual ES produced measurable anterior movement of the tongue. We conclude that when Rph is raised by exogenous means, sublingual transmucosal ES effectively reduces Rph in awake humans.

Expression of the beta-adrenergic receptor-adenylylcyclase system in basal and columnar airway epithelial cells

Catecholamines acting through the beta-adrenergic receptor (beta AR) coupled-adenylylcyclase system stimulate a variety of responses by airway epithelial cells which affect airway caliber and the response to inflammatory stimuli. Although the tracheobronchial epithelium (TBE) is composed of several phenotypically differentiated cell types, surprisingly little is known about the expression of the beta AR system by the major subpopulations of TBE cells (i.e., basal and columnar). We, therefore, examined the function of the beta AR system in columnar and basal cell-enriched populations of rabbit tracheocytes. Cells were collected from 35 rabbits in 17 separate experiments and separated into basal and columnar cell-enriched fractions by centrifugal elutriation. The columnar fraction demonstrated a significantly greater (P < 0.005) adenosine 3',5'-cyclic monophosphate (cAMP) response to isoproterenol (10(-9)-10(-5) M) than the basal cell-enriched fraction (i.e., 74.7 +/- 5.1 and 49.4 +/- 2.8 pmol/10(6) cells, in columnar and basal cell-enriched fractions, respectively, P < 0.0001) as well as a higher beta AR density (i.e., 8,678 +/- 840 and 4,754 +/- 406 beta AR sites/cell, respectively, P < 0.0001). However, when corrected for differences in cell size assessed from measurements of total cell protein, cAMP production per milligram protein and beta AR density per milligram protein were similar in the two cell fractions (P > 0.50 for both comparisons). beta AR subtype assessed by beta 1AR and beta 2AR subtype selective antagonists demonstrated that the beta 2AR subtype predominated (i.e., > 90%) in both cell populations (P > 0.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of beta-agonist- and prostaglandin E2-mediated adenylyl cyclase activity in human airway epithelial cells

Despite the importance of beta 2-adrenergic receptor (beta 2AR) stimulation in mediating airway epithelial cell function, little is known regarding its regulation in airway epithelium. Perturbations of the airway environment associated with disease states, including the management of bronchomotor tone with beta-agonists, expose airways to putative regulators of beta 2AR signal transduction. In this communication, we describe the desensitization of beta 2AR signal transduction in the human airway epithelial cell line BEAS-2B. Examination of both beta-agonist- and prostaglandin E2 (PGE2)-mediated cAMP generation in BEAS-2B cells reveals both agonist-specific (homologous) and non-agonist-specific (heterologous) desensitization of these G protein-coupled receptor pathways. Short-term homologous desensitization of beta 2AR-mediated cAMP generation was characterized by an approximately 60% loss of maximal responsiveness to isoproterenol (ISO) when cells were pretreated 30 min with 10 microM ISO. A reduced sensitivity to ISO was also evidenced by an approximately 4-fold increase in the EC50 for ISO stimulation of adenylyl cyclase (AC). Short-term heterologous desensitization was characterized by an increase in EC50 (approximately 2- to 3-fold) with no change in maximal responsiveness to ISO in cells pretreated with either forskolin or PGE2. Qualitatively similar findings characterized short-term homologous and heterologous desensitization of PGE2-mediated AC activity. Short-term agonist-specific desensitization of the beta 2AR was associated with, but not dependent upon, rapid beta 2AR sequestration. Long-term pretreatment of cells with 10 nM ISO and 1 microM PGE2 eliminated AC responsiveness to subsequent ISO and PGE2 stimulation, respectively. Exposure of BEAS-2B cells to ISO for 24 h resulted in an approximately 70% loss of beta 2ARs, whereas chronic forskolin or PGE2 pretreatment had no effect on beta 2AR number. Long-term pretreatment of cells designed to elicit heterologous desensitization was associated with reductions in maximal responsiveness to ISO and PGE2 that appear to be related to a loss in inherent AC activity. These findings hold strong implications regarding the effect of beta 2AR desensitization on epithelial cell function and the role of beta-agonists in the management of airway disease.

Asthma and diving

BACKGROUND

Approximately 10 to 15 million Americans are scuba divers. The prevalence of scuba diving and asthma makes it likely some asthmatics will be interested in scuba diving and some scuba divers will have asthma. Conditions present during scuba diving may provoke airway obstruction in asthmatic patients. Further, asthmatic patients may, in theory, face a greater than normal risk of pulmonary barotrauma from lung overdistension on ascent through the water column.

OBJECTIVE

The purpose of this paper is to review the theoretical issues underlying the prohibition against scuba diving for asthmatic patients as advanced by most major diving organizations in the United States and critically examine the relevant accident data.

METHODS

All reports that dealt with asthma and diving, and all available American accident data including both fatal and nonfatal accidents were reviewed.

RESULTS

Actuarial data on the risk of scuba accidents attributable to asthma do not define several important variables likely to affect accident risk during scuba diving. Despite these limitations, careful review indicates the risks of serious morbidity or mortality during scuba diving appears to be inconsequentially elevated in subjects whose asthma was not characterized.

CONCLUSIONS

Additional data are needed to define accurately risks of diving in subjects with different forms of asthma, however, the available data suggest asthmatic patients with normal airway function at rest, and with little airway reactivity in response to exercise or cold air inhalation, have a risk of pulmonary barotrauma similar to that of normal subjects.

Respiratory action of the canine deep pectoral muscles

The potential respiratory action of the pectoral muscles is unclear. We studied the effect of electrically stimulated contraction of the deep pectoral muscles on intrathoracic pressure (Pes) and lung volume in 15 supine anesthetized dogs. Changes in Pes and lung volume were also compared with the forelimbs held at the animal's side and elevated 45 degrees to the horizontal plane to alter the mechanical advantage of the deep pectoral muscles. In all animals, bilateral supra-maximal stimulation of the deep pectorals produced negative changes in Pes (-5.9 +/- 0.6 cmH2O) and inspiratory changes in lung volume (324 +/- 44 ml) with the forelimbs elevated. Conversely, in all animals, stimulation of the deep pectorals with the forelimbs at the side produced positive changes in Pes (+ 2.6 +/- 0.2 cmH2O, Plt;0.001) and expiratory changes in lung volume (-113 +/- 16 ml, Plt;0.001). Furthermore, forelimb elevation increased deep pectoral muscle fiber length (mean change 39.9 +/- 7.5% of resting length, Plt;0.001) and reoriented fiber alignment with the rib cage more rostrally. These data indicate that the pectoral muscles exert a respiratory action on the rib cage. Moreover, forelimb posture affects the direction (i.e., inspiratory vs. expiratory) and magnitude of pectoral muscle mechanical action by altering muscle fiber alignment and precontraction length.

Functional behavior of the beta-adrenergic receptor-adenylyl cyclase system in rabbit airway epithelium

Stimulation of adenylyl cyclase mediates the effects of beta-adrenergic agonists and prostaglandin E2 (PGE2) on tracheobronchial epithelial cell function by increasing intracellular cyclic adenosine monophosphate (cAMP). In turn, increases in cAMP affect airway function by modulating ciliary beating, chloride and water transport, mucus secretion, and release of bronchoactive substances. This study examined the function and regulation of the beta-adrenergic receptor-adenylyl cyclase system (beta AR-AC) in tracheal epithelial cells isolated from the rabbit, a frequently used animal model of airway reactivity, inflammation, and electrolyte transport. beta AR number, assessed by ligand binding using the non-subtype-specific beta-antagonist [125I]iodopindolol, averaged approximately 10,700 beta AR/cell (400 fmol/mg membrane protein). Greater than 85% of the receptors were of the beta 2 subtype as determined by competitive antagonist displacement of iodopindolol by selective beta 1- (betaxolol) and beta 2- (ICI 118,551) antagonists. cAMP synthesis was stimulated with isoproterenol, PGE2, and forskolin in a time- and concentration-dependent fashion. Preincubation of epithelial cells for 30 min with either isoproterenol (10 microM) or the peptide inflammatory mediator, bradykinin (100 microM), markedly depressed subsequent isoproterenol-stimulated cAMP synthesis. Isoproterenol-induced beta AR-AC desensitization appeared to be homologous since cAMP responses to PGE2 and forskolin, a direct activator of adenylyl cyclase, were not reduced. The effect of bradykinin on isoproterenol-stimulated cAMP response was mimicked by preincubation with either dioctanoyl glyceride or phorbol myristate acetate, activators of protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization of tracheal epithelium in the cartilaginous portion of adult rabbit and its persistence in organ culture

BACKGROUND

The rabbit trachea provides a model system to test the physiological responses of the airways to various agents. Since three-dimensional organization may affect responses of an organ, an organ culture model was established in serum free medium.

METHODS

Tracheas were fixed in situ, at steps in the preparation of organ cultures, and after one day to three weeks in organ culture. Samples were examined by light microscopy and scanning and transmission electron microscopy for surface morphology, distribution of cell types, and characteristics of the epithelial cell layer.

RESULTS

The normal tracheal mucosa was discovered to consist of extensive circumferential folds in the cartilaginous portion, which were enhanced upon isolation of the trachea from the animal. The folds consisted principally of differences in epithelial cell height rather than folding of the lamina propria. Enhancement of folding upon removal of the trachea coincided with increased secretion by Clara and possibly mucous cells. In organ culture, epithelial cell height initially increased, producing tall folds and cell types were retained in normal proportions. After prolonged culture, cilia were lost but glandular secretion continued.

CONCLUSIONS

Changes in the arrangement of basal cells and secretory activity in isolated trachea and in culture may give insight into the functional significance of the epithelial folds.

Relaxation of rabbit tracheal smooth muscle by adenine nucleotides: mediation by P2-purinoceptors

The relaxant action of adenine nucleotides was studied in isolated rabbit trachealis to assess the presence of P2-purinoceptors in the airways, their cellular location, and pharmacologic properties. Strips of tracheal smooth muscle with intact epithelium were incubated in tissue baths and contracted with 1 microM acetylcholine. Over a dose range of 0.1 microM to 1 mM, ATP and ADP were significantly more potent than adenosine in relaxing tracheal smooth muscle. Significant relaxations were also elicited by AMP-PCP, AMP-CPP, and AMP-PNP, three ATP analogs stable to enzymatic hydrolysis to adenosine. In the absence of acetylcholine, neither ATP nor AMP-CPP exerted any contractile effect on the tracheal strips. In tissues selectively denuded of epithelium, ATP-, ADP-, and AMP-PCP-induced relaxations were markedly reduced. ATP-induced relaxation was also inhibited by the P2y-purinoceptor antagonist Reactive Blue 2 (RB2) (50 to 300 microM) and partially reduced by the cyclooxygenase inhibitor indomethacin (10 microM), whereas adenosine-induced relaxation was not significantly affected by these agents. These results suggest that ATP can induce smooth muscle relaxation in acetylcholine-contracted tracheal strips through a distinct P2-purinoceptor. This receptor appears to be located on the epithelium where its relaxant effect is mediated in part by release of one or more cyclooxygenase products. Additional relaxation at high ATP concentrations may occur through enzymatic hydrolysis of ATP to adenosine and interaction at P1-purinoceptors.