Silver Nanoparticles Alter Cell Adhesion and Proliferation of Sheep Primary Mesothelial Cells.

BACKGROUND: Human exposure to engineered nanoparticles has been linked to pleural effusion, inflammation and fibrosis. Silver nanoparticles (AgNPs) are widely used in medical and domestic products, increasing the risk of occupational and domestic exposure. We assessed the influence of AgNPs on adhesion and proliferation of sheep primary pleural mesothelial cells. MATERIALS AND METHODS: Cells were used for cell adhesion (90 min) and proliferation experiments (3 days) while exposed to 20 nm and 60 nm AgNPs (0.2 µg/ml and 2 µg/ml) using colorimetric assays. RESULTS: Exposure to 0.2 µg/ml of 20 nm and 60 nm AgNPs significantly increased cell adhesion, while at 2 µg/ml this effect was not elicited. Cell proliferation was significantly increased by both 20 nm and 60 nm AgNPs at 0.2 µg/ml, while at 2 µg/ml this effect was only elicited by the 60 nm AgNPs. CONCLUSION: AgNPs alter the adhesive and proliferative properties of primary pleural mesothelial cells.

Silver nanoparticles alter the permeability of sheep pleura and of sheep and human pleural mesothelial cell monolayers.

Nanoparticles have been implicated in the development of pleural effusions in exposed factory workers while in experimental animal studies it has been shown that they induce inflammation, fibrosis and carcinogenesis in the pleura. The scope of this study was to investigate the direct effects of silver nanoparticles exposure on the membrane permeability of sheep parietal pleura, of primary sheep pleural cell monolayers and on a human mesothelial cell line. Our findings suggest that acute (30min) exposure increases the pleural permeability ex vivo, while longer (24h) exposure in vivo leads to late decrease of the pleural cell monolayers permeability.

Influence of AQP1 on cell adhesion, migration, and tumor sphere formation in malignant pleural mesothelioma is substratum- and histological-type dependent.

Malignant pleural mesothelioma (MPM) is an aggressive cancer. MPM cells express aquaporin-1 (AQP1) that in other cancers has been shown to participate in the tumor metastasis processes. However, in MPM patients AQP1 overexpression is an independent prognostic factor favoring survival. In this study we aimed at evaluating the role of AQP1 in cell adhesion, migration, and tumor sphere formation in nonmalignant mesothelial cells (MeT-5A) and in epithelioid (M14K) and sarcomatoid (ZL34) MPM cell lines. We used fibronectin (FN) or homologous cell-derived extracellular martrix (ECM) substratum to investigate the role of AQP1 in these experimental phenotypes, inhibiting AQP1 by 10(-5) M mercury chloride (MC). Deposited ECM during cell culture exhibited significant concentration differences among cell types. ZL34 cell adhesion was significantly higher than MeT-5A or M14K cells on FN and ECM. MeT-5A and M14K cell adhesion on FN was sensitive to AQP1 inhibition, whereas AQP1 inhibition on ECM was limited to M14K cells. Wound healing in ZL34 cells was significantly higher than MeT-5A and M14K cells on FN and ECM. AQP1 inhibition significantly lowered cell migration in ZL34 cells on FN and ECM. Sphere formation was not dependent on FN or ECM in the media. AQP1 inhibition in FN media reduced sphere formation in M14K cells, whereas, in ECM, all three cell types were sensitive to AQP1 inhibition.

Transcriptional over-expression of chloride intracellular channels 3 and 4 in malignant pleural mesothelioma.

BACKGROUND: Chloride Intracellular Channels (CLICs) are contributing to the regulation of multiple cellular functions. CLICs have been found over-expressed in several malignancies, and therefore they are currently considered as potential drug targets. The goal of our study was to assess the gene expression levels of the CLIC's 1-6 in malignant pleural mesothelioma (MPM) as compared to controls. METHODS: We used gene expression data from a publicly available microarray dataset comparing MPM versus healthy tissue in order to investigate the differential expression profile of CLIC 1-6. False discovery rates were calculated and the interactome of the significantly differentially expressed CLICs was constructed and Functional Enrichment Analysis for Gene Ontologies (FEAGO) was performed. RESULTS: In MPM, the gene expressions of CLIC3 and CLIC4 were significantly increased compared to controls (p=0.001 and p<0.001 respectively). A significant positive correlation between the gene expressions of CLIC3 and CLIC4 (p=0.0008 and Pearson's r=0.51) was found. Deming regression analysis provided an association equation between the CLIC3 and CLIC4 gene expressions: CLIC3=4.42CLIC4-10.07. CONCLUSIONS: Our results indicate that CLIC3 and CLIC4 are over-expressed in human MPM. Moreover, their expressions correlate suggesting that they either share common gene expression inducers or that their products act synergistically. FAEGO showed that CLIC interactome might contribute to TGF beta signaling and water transport.

Computational genomic analysis of PARK7 interactome reveals high BBS1 gene expression as a prognostic factor favoring survival in malignant pleural mesothelioma.

The aim of our study was to assess the differential gene expression of Parkinson protein 7 (PARK7) interactome in malignant pleural mesothelioma (MPM) using data mining techniques to identify novel candidate genes that may play a role in the pathogenicity of MPM. We constructed the PARK7 interactome using the ConsensusPathDB database. We then interrogated the Oncomine Cancer Microarray database using the Gordon Mesothelioma Study, for differential gene expression of the PARK7 interactome. In ConsensusPathDB, 38 protein interactors of PARK7 were identified. In the Gordon Mesothelioma Study, 34 of them were assessed out of which SUMO1, UBC3, KIAA0101, HDAC2, DAXX, RBBP4, BBS1, NONO, RBBP7, HTRA2, and STUB1 were significantly overexpressed whereas TRAF6 and MTA2 were significantly underexpressed in MPM patients (network 2). Furthermore, Kaplan-Meier analysis revealed that MPM patients with high BBS1 expression had a median overall survival of 16.5 vs. 8.7 mo of those that had low expression. For validation purposes, we performed a meta-analysis in Oncomine database in five sarcoma datasets. Eight network 2 genes (KIAA0101, HDAC2, SUMO1, RBBP4, NONO, RBBP7, HTRA2, and MTA2) were significantly differentially expressed in an array of 18 different sarcoma types. Finally, Gene Ontology annotation enrichment analysis revealed significant roles of the PARK7 interactome in NuRD, CHD, and SWI/SNF protein complexes. In conclusion, we identified 13 novel genes differentially expressed in MPM, never reported before. Among them, BBS1 emerged as a novel predictor of overall survival in MPM. Finally, we identified that PARK7 interactome is involved in novel pathways pertinent in MPM disease.

Airways microbiota: Hidden Trojan horses in asbestos exposed individuals?

Malignant pleura mesothelioma (MPM) is a rare type of cancer with devastating prognosis, which develops in the pleural cavity from transformed mesothelium. MPM has been directly associated with asbestos exposure however there are aspects of the pathophysiology involved in the translocation of asbestos fibers in the pleura that remain unclear. Here, we propose and discuss that certain proteins secreted by airways symbiotic microbiota create membrane pores to the airway epithelial cells, through which asbestos fibers can penetrate the lung parenchyma and reach the sub-pleural areas. We evaluate this hypothesis using data from the published literature regarding the airways microbiota toxins such as cholesterol-dependent cytolysins (CDCs).

VEGF increases the permeability of sheep pleura ex vivo through VEGFR2 stimulation.

Vascular endothelial growth factor (VEGF), a cytokine that increases vascular permeability to water and proteins and induces angiogenesis, has been implicated in the development of pleural effusions. Inflammatory and malignant pleural effusions are rich in VEGF content while mesothelial cells produce and excrete VEGF. In this report we aimed at investigating by means of electrophysiology the direct effects of VEGF on the parietal and visceral sheep pleura as well as the type of receptors that mediate this effect. Our findings show that VEGF has a direct effect on the pleural mesothelium rendering it more permeable and this effect is mediated through the stimulation of VEGF receptor 2. Our findings shed more light to the role of VEGF in the pathogenesis of pleural effusions and provide functional evidence for a role of VEGFR2 on the pleural mesothelium that has never been studied before.

Ranolazine enhances the antiarrhythmic activity of amiodarone by accelerating conversion of new-onset atrial fibrillation after cardiac surgery.

Ranolazine is a relatively novel antiischemic/antianginal compound with antiarrhythmic properties. We investigated its ability to shorten the time to conversion of postoperative atrial fibrillation (POAF) when added to amiodarone after coronary artery bypass graft (CABG) surgery. In this prospective, randomized, allocation-concealed, single-blind, single-site clinical trial, we enrolled consecutive eligible patients who developed POAF after elective on-pump CABG surgery. Participants were randomized to receive either ranolazine 375 mg twice daily orally plus intravenous amiodarone (active group) or intravenous amiodarone alone (control group). We enrolled 41 patients; 20 in the active and 21 in the control group. There were no significant differences between the groups in terms of age, procedural duration, extracorporeal circulation time, and aortic cross-clamp time. Mean time of conversion was significantly shorter in the active group (19.9 ± 3.2 vs 37.2 ± 3.9 hours, P < .001), suggesting that compared to amiodarone alone, the ranolazine-amiodarone combination had a superior antiarrhythmic effect against POAF.

TNFα induces expression of HIF-1α mRNA and protein but inhibits hypoxic stimulation of HIF-1 transcriptional activity in airway smooth muscle cells.

Airway smooth muscle cells (ASMCs) participate in tissue remodeling characteristic of airway inflammatory diseases like asthma. Inflammation and hypoxia pathways are often interconnected and the regulatory subunit of the hypoxia inducible factor, HIF-1α, has been recently shown to be induced by cytokines. Here we investigate the effect of individual or combined treatment of ASMCs with the inflammatory mediator TNFα and/or hypoxia on the expression of HIF-1α, HIF-1 targets and inflammation markers. TNFα enhances HIF-1α protein and mRNA levels, under both normoxia and hypoxia. TNFα-mediated induction of HIF-1α gene transcription is repressed by inhibition of the NF-κB pathway. Despite the up-regulation of HIF-1α protein, the transcription of HIF-1 target genes remains low in the presence of TNFα at normoxia and is even reduced at hypoxia. We show that the reduction in HIF-1 transcriptional activity by TNFα is due to inhibition of the interaction of HIF-1α with ARNT and subsequent blocking of its binding to HREs. Comparison between hypoxia and TNFα for their effects on the expression of inflammatory markers shows significant differences: hypoxia up-regulates the expression of IL-6, but not RANTES or ICAM, and reduces the induction of VCAM by TNFα. Finally, ex vivo treatment of rabbit trachea strips with TNFα increases HIF-1α protein levels, but reduces the expression of HIF-1 targets under hypoxia. Overall, TNFα induces HIF-1α mRNA synthesis via an NF-κB dependent pathway but inhibits binding of HIF-1α to ARNT and DNA, while hypoxia and TNFα have distinct effects on ASMC inflammatory gene expression.

Gene expression profile of aquaporin 1 and associated interactors in malignant pleural mesothelioma.

Overexpression of AQP1 has recently been shown to be an independent prognostic factor in pleural mesothelioma favoring survival. This paper presents a data mining and bioinformatics approach towards the evaluation of the gene expression profile of AQP1 in malignant pleural mesothelioma and of AQP1 associated markers in the context of mesothelioma disease phenotype, CDKN2A gene deletion, sex and asbestos exposure. The data generated were thus again subjected to differential expression profile analysis. Here we report that AQP1 is overexpressed in epithelioid mesothelioma and identify TRIP6 and EFEMP2 as candidate genes for further investigation in mesothelioma.

Endothelial progenitor cells in the pathogenesis of idiopathic pulmonary fibrosis: an evolving concept.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) has been associated with abnormal vascular remodeling. Bone marrow derived endothelial progenitor cells (EPCs) are considered to possess lung tissue repair and vascular remodeling properties. OBJECTIVES: The study aimed to assess early EPCs levels and EPCs endogenous vascular endothelial growth factor (VEGF) expression in IPF. In order to examine alterations in the mobilization of EPCs from the bone marrow we measured plasma VEGF. MAIN RESULTS: Twenty-three patients with IPF and fifteen healthy subjects were included. The number of early EPCs colonies was markedly reduced in IPF patients vs controls (6.00±6.49 vs 49.68±16.73, respectively, p<0.001). EPCs were further decreased in patients presenting systolic pulmonary arterial pressure (sPAP)≥35 mmHg. The number of colonies per well correlated negatively with P((A-a))O(2) (r =  -0.750, p<0.001). Additionally, VEGF mRNA levels were significantly increased in IPF patients. There were no differences observed in VEGF plasma levels in IPF patients when compared to controls. CONCLUSIONS: The current data suggest that inadequate levels of early EPCs may potentially contribute to suppressed repair and recovery of the damaged pulmonary endothelium and thereby may drive the sequence of events in profibrogenic direction. Increased VEGFmRNA levels in the clinical context of IPF may represent a compensatory mechanism to overcome reduced EPCs levels.

Pleural fluid protein is inversely correlated with age in uncomplicated parapneumonic pleural effusions.

OBJECTIVES: Assess whether age influences standard biochemical parameters used in the differential diagnosis of transudative and exudative pleural effusions. DESIGN AND METHODS: We retrospectively analyzed data from the database of our clinic from 225 patients with pleural effusions categorized based on their final diagnosis in 5 groups: transudates 41 (18%), uncomplicated parapneumonic 26 (12%), complicated parapneumonic 20 (9%), tuberculosis 35 (15%) and lung cancer 103 (46%). We tested whether age correlated with pleural fluid protein or lactate dehydrogenase. RESULTS: There was a statistically significant inverse correlation only between the age and the pleural fluid protein content in patients with uncomplicated parapneumonic effusions with correlation coefficient r=-0.6 [(95% CI=-0.8 to -0.28); p=0.001]. Linear regression analysis showed that this association is given by the equation: age=101.998-10.03 protein. In the same group of patients age was not correlated with serum protein content. CONCLUSIONS: Our study shows that age may be a confounding factor in the differential diagnosis of transudative and exudative pleural effusions. Clinicians should be aware of this finding especially when dealing with elders.

Effect of ranolazine in preventing postoperative atrial fibrillation in patients undergoing coronary revascularization surgery.

BACKGROUND/OBJECTIVE: Ranolazine is a new anti-ischemic agent approved for chronic angina with additional electrophysiologic properties. The purpose of the present trial was to investigate its effect in preventing postoperative atrial fibrillation (POAF) after on-pump coronary artery bypass graft (CABG) surgery. METHODS: In the current prospective, randomized, (1 active: 2 control), single-blind (outcome assessors), single-centre clinical trial we recruited consecutive eligible patients scheduled for elective on-pump CABG. Participants were assigned to receive either oral ranolazine 375 mg twice daily for 3 days prior to surgery and until discharge, or to receive usual care. Patients were monitored for the development of POAF. RESULTS: We enrolled 102 patients. Significantly lower incidence of POAF was noted in the ranolazine group compared with the control group (3 out of 34 patients, 8.8%, vs 21 out of 68 patients, 30.8%; p< 0.001). Mean values of left atrial diameter and left ventricular ejection fraction between the control and the ranolazine group were not significantly different. CONCLUSION: Our findings suggest a protective role of oral ranolazine when administered in a moderate dose preoperatively in patients undergoing on-pump CABG surgery. Future studies based on a wider sample of patients will eventually support our conclusions.

Permeability of the arachnoid and pia mater. The role of ion channels in the leptomeningeal physiology.

PURPOSE: The purpose of this paper is to study the ionic permeability of the leptomeninges related to the effect of ouabain (sodium-potassium-ATPase inhibitor) and amiloride (epithelial sodium channel (ENaC) inhibitor) on the tissue, as well as identify the presence of ion channels. METHODS: Cranial leptomeningeal samples from 26 adult sheep were isolated. Electrophysiological measurements were performed with Ussing system and transmembrane resistance values (R(TM) in Ω*cm(2)) obtained over time. Experiments were conducted with the application of ouabain 10(-3) M or amiloride 10(-5) M at the arachnoidal and pial sides. Immunohistochemical studies of leptomeningeal tissue were prepared with alpha-1 sodium-potassium-ATPase (ATP1A1), beta-ENaC, and delta-ENaC subunit antibodies. RESULTS: The application of ouabain at the arachnoidal side raised the transmembrane resistance statistically significantly and thus decreased its ionic permeability. The addition of ouabain at the pial side led also to a significant but less profound increment in transmembrane resistance. The addition of amiloride at the arachnoidal or pial side did not produce any statistical significant change in the R(TM) from controls (p > 0.05). Immunohistochemistry confirmed the presence of the ATP1A1 and beta- and delta-ENaC subunits at the leptomeninges. CONCLUSIONS: In summary, leptomeningeal tissue possesses sodium-potassium-ATPase and ENaC ion channels. The application of ouabain alters the ionic permeability of the leptomeninges thus reflecting the role of sodium-potassium-ATPase. Amiloride application did not alter the ionic permeability of leptomeninges possibly due to localization of ENaC channels towards the subarachnoid space, away from the experimental application sites. The above properties of the tissue could potentially be related to cerebrospinal fluid turnover at this interface.

Pleural transport physiology: insights from biological marker measurements in transudates.

AIMS: The aim of this study was to evaluate the physicochemical properties of the pleural mesothelial barrier and of the biological markers that facilitate or eliminate the passage of molecules through the pleura. METHODS AND MATERIAL: Pleural fluid samples from sixty-five patients with heart failure were analyzed. The biological markers studied were lactate dehydrogenase (LDH), adenosine deaminase (ADA), interleukin-6 (IL-6), C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), carcinoembryonic antigen (CEA), copper/zinc superoxide dismutase (CuZnSOD), matrix metalloproteinase-2 (MMP-2), -3 (MMP-3), -7(MMP-7), -8 (MMP-8) and -9 (MMP-9). Based on the pleural fluid/serum ratio, these molecules were divided into three groups: a) the LDH-like group with a pleural fluid/serum ratio between 0,4 and 0,8 (LDH, CEA, CuZnSOD, ADA, CRP, MMP-8), b) molecules with a pleural fluid/serum ratio less than 0,4 (MMP-7 and MMP-9) and c) molecules with a pleural fluid/serum ratio equal or above 1 (TNF-α, IL-6, MMP-2 and MMP-3). RESULTS: No correlation between the molecular radius and the pleural fluid to serum ratio of the above biological markers was found. CONCLUSIONS: The molecular size is not a major determinant for the passage of molecules through the mesothelial barrier. Several other factors may influence the transport of the above molecules to pleural cavity, such as their charge and shape.

The mitogenic effect of testosterone and 17ß-estradiol on airway smooth muscle cells.

Airway disease distribution and/or severity exhibit sex differences suggesting that sex hormones are involved in the respiratory system physiology and pathophysiology. The implication of airway smooth muscle cells (ASMCs) in the physiology of the airways and the pathogenetic mechanism of airway remodeling is of great interest. Therefore, we studied the effect of testosterone and 17ß-estradiol on ASMC proliferation and the mechanisms involved. Cell proliferation was estimated using the methyl-[³H]thymidine incorporation and Cell Titer 96® AQueous One Solution Assay methods. ASMC isolated from adult male or female rabbit trachea were incubated with testosterone (1 pM-1 µM) or 17ß-estradiol (1 pM-1 µM), in the presence or absence of the androgen receptor antagonist flutamide (10 nM) or estrogen receptor antagonist ICI182780 (10 nM), as well as of the PI3K inhibitors LY294002 (20 µM) or wortmannin (1 µM), or the MAPK inhibitors PD98059 (100 µM) or U0126 (1 µM). After 24 h of incubation, testosterone and 17ß-estradiol increased methyl-[³H]thymidine incorporation and cell number, in ASMC isolated from male or female animals. The induction of ASMC proliferation by testosterone or 17ß-estradiol was inhibited by flutamide or ICI182780 respectively, as well as by LY294002, wortmannin, PD98059 or U0126. In conclusion, testosterone and 17ß-estradiol have a mitogenic effect on ASMC, which is receptor-mediated and involves the MAPK and PI3K signaling pathways. Moreover, their effect is the same for ASMC from male and female animals. It is possible that gender-related differences in ASMC remodeling, may be influenced by the different patterns of sex steroid hormone secretion in males and females.

Effect of sodium-potassium pump inhibition by ouabain on the permeability of isolated visceral sheep peritoneum.

The permeability for small solutes and the ultrafiltration capacity of the peritoneum are essential for effective peritoneal dialysis (PD) treatment. Elucidation of the factors that regulate these two properties is therefore of great importance. Ouabain, a potent inhibitor of the Na+-K+ pump has been shown to reduce fluid absorption in animal models of PD. In the present study, we used Ussing chamber experiments to investigate the effect of ouabain on the transmesothelial electrical resistance (RTM) of isolated visceral sheep peritoneum. Peritoneal samples from the omentum of adult sheep were isolated immediately after the deaths of the animals and were transferred to the laboratory in cooled Krebs-Ringer bicarbonate solution (4 degrees C, pH 7.5) bubbled with 95% O2/5% CO2. A planar sheet of visceral peritoneum was mounted in an Ussing-type chamber, and ouabain (10(-3) mol/L) was added apically and basolaterally. The RTM was measured before and serially for 30 minutes after the addition of ouabain. Because active ion transport is temperature-dependent, all measurements were taken at 37 degrees C. The results presented are the mean +/- standard error of 6 experiments. Before the addition of ouabain, the control RTM was measured as 21.26 +/- 0.57 Omega x cm2. Addition of ouabain basolaterally induced an increase in the RTM to 27.62 +/- 0.72 Omega x cm2 within 1 minute (p < 0.05), and this level persisted throughout the experiment. The effect of ouabain, when added apically, was similar, characterized by a rapid rise in the RTM to 24.66 +/- 0. 76 Omega x cm2 at 1 minute (p < 0. 05), with subsequent persistence at that level. A clear association between RTM and active ion transport has been shown in previous studies. The results of the present study, showing a rapid effect of ouabain on the RTM of visceral peritoneum, therefore clearly suggest that cell membrane Na+K+-ATPase is important for peritoneal ionic transport. In addition, ouabain was previously shown to reduce vasodilation and intraperitoneal sodium or to increase intraperitoneal volume, especially in the presence of conventional acidic solutions. Those findings, combined with the results of the present study, clearly indicate that intraperitoneal administration of digitalis glycosides may have some beneficial effect in PD patients; however the specific clinical implications need further investigation.

The contribution of ascorbic acid and dehydroascorbic acid to the protective role of pleura during inflammatory reactions.

It is well-known that parapneumonic effusions lead to the formation of inflammatory exudates which contain an increasing amount of inflammatory cells, especially polymorphonuclear. At these pathological conditions characterized by oxidative stress, ascorbic acid (AA) plays an important role in quenching free radicals, so that it could protect neutrophils and mesothelial cells from oxidative damage. Besides that ascorbic acid and its metabolite dehydroascorbic acid (DHA) alters the sheep visceral and parietal pleura permeability. More specific ascorbic acid as well as dehydroascorbic acid decreases the permeability of pleura after addition on apical and basolateral side in both visceral and parietal pleurae. It seems that, AA and DHA have an opposite action upon pleura from that of the inflammatory mediators, like VEGF, which increases the permeability of pleura and causes mesothelial barrier dysfunction. The decrease of pleura permeability induced by AA and DHA suggest the hypothesis that AA and/or its metabolite DHA during inflammatory reactions not only protects mesothelial cells from oxidative damage, but also contributes to maintaining the mesothelial barrier function. Consequently, the inflammatory pleural fluid may be trapped in pleural space and the inflammation may be restricted, and have extension avoided.

Azithromycin has a direct relaxant effect on precontracted airway smooth muscle.

Macrolides have been proven to have beneficial bacteriostatic and anti-inflammatory properties, but very little is known about the potential value of their bronchodilatory effect. Therefore, in the present study we investigated the effect of azithromycin on contractile responses of isolated rabbit tracheal strips to carbachol or KCl. Azithromycin has a relaxant, concentration-dependent effect on tracheal strips precontracted with carbachol (300 nM), significant from the concentration of 1 muM. The mechanical removal of epithelium did not alter the effect of azithromycin. Azithromycin (100 microM) also relaxed tracheal strips precontracted with KCl (80 mM) even in the presence of atropine (100 microM). Moreover, azithromycin (100 microM) decreased contractions induced by 300 nM and 10 microM carbachol to 55.4% and 80.5% of initial contraction, respectively. The relaxant effect of azithromycin persisted in both calcium free solution and in the presence of the calcium channel antagonist, verapamil. The relaxant effect of azithromycin was not altered by the pre-treatment of preparations with the inhibitors of Ca(2+)-ATPase (cyclopiazonic acid), Na(+)-K(+) ATPase (ouabain), Rho-associated kinase [(R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride] (Y-27632) or the non-specific cAMP and cGMP phosphodiesterases inhibitor 3-isobutyl-1-methyl-2,6(1H,3H)-purinedione (IBMX). These results suggest that azithromycin has a concentration-dependent, epithelium-independent, direct relaxant effect on precontracted tracheal strips that is not mediated via inhibition of Ca(2+) influx or Ca(2+) release from intracellular stores. Also, it is not due to alteration of the function of Na(+)-K(+) ATPase and does not depend on the formation of cAMP/cGMP or the Rho/Rho-activated kinase pathway.