Airway epithelium: more than just a barrier!

PM2.5 Aggravated OVA-Induced Epithelial Tight Junction Disruption Through Fas Associated via Death Domain-Dependent Apoptosis in Asthmatic Mice

BACKGROUND

Exposure to air pollutants cause exacerbation of asthma, but the experimental evidence and the mechanisms still need to be collected and addressed.

METHODS

Asthma model was constructed by ovalbumin (OVA) combined with or without airborne fine particulate matter 2.5 (PM2.5) exposure. Lung sections were stained by hematoxylin-eosin staining (H&E) and Masson's trichrome. RNA-seq and gene set enrichment analysis (GSEA) was performed to identify the key pathway. TdT mediated dUTP Nick End Labeling (TUNEL) assay, real-time qPCR, Western blot, immunofluorescence and lentivirus transfection were applied for mechanism discovery.

RESULTS

In this study, we found PM2.5 aggravated airway inflammation in OVA-induced asthmatic mice. RNA-seq analysis also showed that epithelial mesenchymal transition (EMT) was enhanced in OVA-induced mice exposed to PM2.5 compared with that in OVA-induced mice. In the meantime, we observed that apoptosis was significantly increased in asthmatic mice exposed to PM2.5 by using GSEA analysis, which was validated by TUNEL assay. By using bioinformatic analysis, Fas associated via death domain (FADD), a new actor in innate immunity and inflammation, was identified to be related to apoptosis, EMT and tight junction. Furthermore, we found that the transcript and protein levels of tight junction markers, E-cadherin, zonula occludens (ZO)-1 and Occludin, were decreased after PM2.5 exposure in vivo and in vitro by using RT-qPCR and immunofluorescence, with the increased expression of FADD. Moreover, down-regulation of FADD attenuated PM2.5-induced apoptosis and tight junction disruption in human airway epithelial cells.

CONCLUSION

Taken together, we demonstrated that PM2.5 aggravated epithelial tight junction disruption through apoptosis mediated by up-regulation of FADD in OVA-induced model.

Fueling influenza and the immune response: Implications for metabolic reprogramming during influenza infection and immunometabolism

Recent studies support the notion that glycolysis and oxidative phosphorylation are rheostats in immune cells whose bioenergetics have functional outputs in terms of their biology. Specific intrinsic and extrinsic molecular factors function as molecular potentiometers to adjust and control glycolytic to respiratory power output. In many cases, these potentiometers are used by influenza viruses and immune cells to support pathogenesis and the host immune response, respectively. Influenza virus infects the respiratory tract, providing a specific environmental niche, while immune cells encounter variable nutrient concentrations as they migrate in response to infection. Immune cell subsets have distinct metabolic programs that adjust to meet energetic and biosynthetic requirements to support effector functions, differentiation, and longevity in their ever-changing microenvironments. This review details how influenza coopts the host cell for metabolic reprogramming and describes the overlap of these regulatory controls in immune cells whose function and fate are dictated by metabolism. These details are contextualized with emerging evidence of the consequences of influenza-induced changes in metabolic homeostasis on disease progression.

Regulation of smooth muscle contractility by the epithelium in rat tracheas: role of prostaglandin E2 induced by the neurotransmitter acetylcholine

Background

Previous studies have suggested the involvement of epithelium in modulating the contractility of neighboring smooth muscle cells. However, the mechanism underlying epithelium-derived relaxation in airways remains largely unclear. This study aimed to investigate the mechanism underlying epithelium-dependent smooth muscle relaxation mediated by neurotransmitters.

Methods

The contractile tension of Sprague-Dawley (SD) rat tracheal rings were measured using a mechanical recording system. Intracellular Ca²⁺ level was measured using a Ca²⁺ fluorescent probe Fluo-3 AM, and the fluorescence signal was recorded by a laser scanning confocal imaging system. The prostaglandin E₂ (PGE₂) content was measured using an enzyme-linked immunosorbent assay kit.

Results

We observed that the neurotransmitter acetylcholine (ACh) restrained the electric field stimulation (EFS)-induced contraction in the intact but not epithelium-denuded rat tracheal rings. After inhibiting the muscarinic ACh receptor (mAChR) or cyclooxygenase (COX), a critical enzyme in prostaglandin synthesis, the relaxant effect of ACh was attenuated. Exogenous PGE₂ showed a similar inhibitory effect on the EFS-evoked contraction of tracheal rings. Moreover, ACh triggered phospholipase C (PLC)-coupled Ca²⁺ release from intracellular Ca²⁺ stores and stimulated COX-dependent PGE₂ production in primary cultured rat tracheal epithelial cells.

Conclusions

Collectively, this study demonstrated that ACh induced rat tracheal smooth muscle relaxation by promoting PGE₂ release from tracheal epithelium, which might provide valuable insights into the cross-talk among neurons, epithelial cells and neighboring smooth muscle cells in airways.

The protective effect of doxofylline against lipopolysaccharides (LPS)-induced activation of NLRP3 inflammasome is mediated by SIRT1 in human pulmonary bronchial epithelial cells

Lung diseases are common health problems in many countries. The dysfunction of bronchial epithelial cells is important for the development of lung diseases. Recent progress reveals that inflammasome is the fundamental mechanism of epithelial activation. Here, we report the protective effect of doxofylline, a theophylline derivative agent, on lipopolysaccharides (LPS)-induced inflammatory response in bronchial epithelial cells. The presence of doxofylline reduces LPS-induced production of NO and PGE₂. Doxofylline also inhibits LPS-induced production of mitochondrial ROS. Mechanistically, we show that doxofylline suppresses the expression of NOX4 induced by LPS. Doxofylline inhibits LPS-induced NLRP3-TXNIP inflammasome activation as revealed by its inhibitive effect on NLRP3, caspase 1 (P10 unit), and TXNIP induction as well as weakened induction of IL-1β and IL-18. Furthermore, we show that doxofylline ameliorates LPS-induced Sirtuin 1 (SIRT1) reduction. The silencing of SIRT1 abolishes the inhibitory effect of doxofylline on NLRP3 inflammasome activation. Collectively, our study demonstrates that doxofylline mitigates epithelial inflammation via amelioration of multiple cellular pathways, including NLRP3-TXNIP inflammasome activation.

Anti-Bronchospasmodic Effect of JME-173, a Novel Mexiletine Analog Endowed With Highly Attenuated Anesthetic Activity

Local anesthetics (LAs), such as lidocaine and mexiletine, inhibit bronchoconstriction in asthmatics, but adverse effects limit their use for this specific clinical application. In this study, we describe the anti-spasmodic properties of the mexiletine analog 2-(2-aminopropoxy)-3,5-dimethyl, 4-Br-benzene (JME-173), which was synthesized and screened for inducing reduced activity on Na⁺ channels. The effectiveness of JME-173 was assessed using rat tracheal rings, a GH3 cell line and mouse cardiomyocytes to access changes in smooth muscle contraction, and Na⁺, and Ca⁺⁺ionic currents, respectively. Bronchospasm and airway hyper-reactivity (AHR) were studied using whole-body barometric plethysmography in A/J mice. We observed that the potency of JME-173 was 653-fold lower than mexiletine in inhibiting Na⁺ currents, but 12-fold higher in inhibiting L-type Ca⁺⁺ currents. JME-173 was also more potent than mexiletine in inhibiting tracheal contraction by carbachol, allergen, extracellular Ca⁺⁺, or sodium orthovanadate provocations. The effect of JME-173 on carbachol-induced tracheal contraction remained unaltered under conditions of de-epithelized rings, β₂-receptor blockade or adenylate cyclase inhibition. When orally administered, JME-173 and theophylline inhibited methacholine-induced bronchospasm at time points of 1 and 3 h post-treatment, while only JME-173 remained active for at least 6 h. In addition, JME-173 also inhibited AHR in a mouse model of lipopolysaccharide (LPS)-induced lung inflammation. Thus, the mexiletine analog JME-173 shows highly attenuated activity on Na⁺ channels and optimized anti-spasmodic properties, in a mechanism that is at least in part mediated by regulation of Ca⁺⁺ inflow toward the cytosol. Thus, JME-173 is a promising alternative for the treatment of clinical conditions marked by life-threatening bronchoconstriction.

Protective Effect of GHX02 Extract on Particulate Matter-Induced Lung Injury

Industrial development, along with the rapid growth of the economy, has greatly improved the quality of life in humans. Moreover, advancements in medical technology have increased life expectancy. Small particles increase airway inflammation when they penetrate the alveoli. We observed that GHX02 decreased the frequency and delayed the onset time of citric acid-induced coughing in guinea pigs. A phenol red secretion assay indicated that the GHX02 extract exhibits potent expectorant activity. The GHX02 extract also greatly reduced leukocyte levels. Our results indicate that GHX02 inhibits airway inflammation, reduces sputum production, and relieves cough. The GHX02 extract suppressed histamine release from mast cells resulting from compound 48/80-induced degranulation. The extract exhibited antimicrobial activity against Streptococcus pneumoniae and significantly inhibited the formation of LTC4. At high concentrations, the GHX02 extract suppressed the formation of PGE2 (prostaglandin E2). Interleukin (IL)-4 and IL-13 levels decreased with an increasing dosage of GHX02. Oral administration of the GHX02 extract suppressed PM₁₀D-induced inflammatory symptoms in the lung, including increased alveolar wall thickness, accumulation of collagen fibers, and cytokine release. Treatment with the GHX02 extract also resulted in lower levels of inflammatory cells, in bronchoalveolar lavage fluid and lung tissue. Our results indicate that GHX02 may be a useful therapeutic agent for treatment of respiratory diseases.

Naringin and Naringenin Relax Rat Tracheal Smooth by Regulating BKCa Activation

Naringin and its aglycone, naringenin, occur naturally in our regular diet and traditional Chinese medicines. This study aimed to detect an effective therapeutic approach for cough variant asthma (CVA) through evaluating the relaxant effect of these two bioactive herbal monomers as antitussive and antiasthmatic on rat tracheal smooth muscle. The relaxant effect was determined by measuring muscular tension with a mechanical recording system in rat tracheal rings. Cytosolic Ca²⁺ concentration was measured using a confocal imaging system in primary cultured tracheal smooth muscle cells. In rat tracheal rings, addition of both naringin and naringenin could concentration dependently relax carbachol (CCh)-evoked tonic contraction. This epithelium-independent relaxation could be suppressed by BaCl₂, tetraethylammonium, and iberiotoxin (IbTX), but not by glibenclamide. After stimulating primary cultured tracheal smooth muscle cells by CCh or high KCl, the intracellular Ca²⁺ increase could be inhibited by both naringin and naringenin, respectively. This reaction was also suppressed by IbTX. These results demonstrate that both naringin and naringenin can relax tracheal smooth muscle through opening big conductance Ca²⁺-activated K⁺ channel, which mediates plasma membrane hyperpolarization and reduces Ca²⁺ influx. Our data indicate a potentially effective therapeutic approach of naringin and naringenin for CVA.

Antiasthmatic activity of quercetin glycosides in neonatal asthmatic rats

The present study investigated the anti-asthmatic activity of quercetin glycosides in neonatal asthmatic rats. Rats were divided into four groups: sham (non-asthmatic), asthmatic control, quercetin (25 mg/kg), and quercetin (50 mg/kg). Inflammatory cells in bronchoalveolar lavage fluid (BALF), inflammatory markers, apoptosis, fibrinogen level, prothrombin time, thrombin time, activated partial thromboplastin time, coagulation factor activity, and histopathology were monitored. Quercetin significantly reduced total leukocytes, eosinophils, tumor necrosis factor-α (TNF-α), interleukin (IL-6), nitric oxide (NO), and apoptosis. It also considerably reduced blood coagulation time and coagulation factor activity compared to the controls. The mRNA expression levels of TNF-α, IL-6, and inducible nitric oxide synthase (iNOS) were elevated in asthmatic rats by 1.3-, 1.04-, and 1.1-fold, respectively. However, treatment with 50 mg/kg quercetin glycosides significantly reduced the mRNA expression of TNF-α, IL-6, and iNOS by more than 40%. Quercetin considerably reduced the protein expression of iNOS. Airway and blood vessel narrowing, as well as the accumulation of eosinophils in the lungs were observed in neonatal asthmatic rats. However, treatment with quercetin glycosides significantly reduced inflammation and eosinophil infiltration. In summary, quercetin glycosides significantly attenuated levels of inflammatory markers, demonstrating its protective effects against neonatal asthma in rats.

lncRNA Malat1 modulates the maturation process, cytokine secretion and apoptosis in airway epithelial cell-conditioned dendritic cells

Airway epithelial cells (AECs) are the first point of contact with airborne antigens and are able to instruct resident immune cells to appropriate immune responses. Previous studies have shown that the abnormal expression of metastasis-associated lung adenocarcinoma transcript 1 (Malat1) was associated with tumorigenesis, progression, metastasis, and apoptosis in many cancer types. However, little is known about its functional involvement in the cross-talk of AECs with dendritic cells (DCs). The aim of the present study was to identify Malat1 as a novel epithelial cell-derived immune-modulating factor that contributes to the specific inflammatory-immune airway microenvironment. By using an in vitro co-culture model, where layers of AECs can interact with DCs, and transfecting Malat1 siRNA in AECs, AEC-conditioned DCs were harvested for further analysis of the celluar phenotype, secretion of inflammatory chemokines, and expression of apoptotic markers. The present study clearly demonstrated that Malat1 modulates the maturation process, pro-inflammatory cytokine secretion and apoptosis in AECs-conditioned DCs.

Physiology of nitric oxide in the respiratory system

Nitric oxide (NO) is an important endogenous neurotransmitter and mediator. It participates in regulation of physiological processes in different organ systems including airways. Therefore, it is important to clarify its role in the regulation of both airway and vascular smooth muscle, neurotransmission and neurotoxicity, mucus transport, lung development and in the. surfactant production. The bioactivity of NO is highly variable and depends on many factors: the presence and activity of NO-producing enzymes, activity of competitive enzymes (e.g. arginase), the amount of substrate for the NO production, the presence of reactive oxygen species and others. All of these can change NO primary physiological role into potentially harmful. The borderline between them is very fragile and in many cases not entirely clear. For this reason, the research focuses on a comprehensive understanding of NO synthesis and its metabolic pathways, genetic polymorphisms of NO synthesizing enzymes and related effects. Research is also motivated by frequent use of exhaled NO monitoring in the clinical manifestations of respiratory diseases. The review focuses on the latest knowledge about the production and function of this mediator and understanding the basic physiological processes in the airways.

Deterioration of epithelium mediated mechanisms in diabetic-antigen sensitized airways of guinea pigs

BACKGROUND

The onset of diabetes causes disruption of respiratory epithelial mediators. The present study investigates whether diabetes modifies the epithelium mediated bronchial responses in hyper-reactive airway smooth muscle (ASM) primarily through nitric oxide (NO), cyclooxygenase (COX), and epithelium derived hyperpolarizing factor (EpDHF) pathways.

METHODS

Experimental model of guinea pigs having hyper-reactive airways with or without diabetes were developed. The responses of tracheal rings to cumulative concentrations of acetylcholine (ACh) and isoproterenol (IP) in the presence and absence of epithelium and before and after incubation with NO, K⁺_ATP and COX inhibitors, N-(ω)-Nitro-L-arginine methyl ester (L-NAME; 100 μM), glybenclamide (10 μM) and indomethacin (100 μM) were assessed.

RESULTS

In diabetic guinea pigs with hyper-reactive airways, a decrease in ACh induced bronchoconstriction was observed after epithelium removal and after incubation with L-NAME/indomethacin, suggesting damage to NO/COX pathways. Hyper-reactivity did not alter the response of trachea to ACh but affected the response to IP which was further reduced in hyper-reactive animals with diabetes. The ASM response to IP after glybenclamide treatment did not alter in hyper-reactive guinea pigs and diabetic guinea pigs with hyper-reactive airways, suggesting damage to the EpDHF pathway. Treatment with indomethacin reduced IP response in the hyper-reactive model, and did not produce any change in diabetic model with hyper-reactive airways, indicating further disruption of the COX pathway.

CONCLUSION

EpDHF pathway is damaged in hyper-reactive guinea pigs and in diabetic guinea pigs with hyper-reactive airways. Diabetes further aggravates the NO and COX mediated pathways in diabetic guinea pigs with hyper-reactive airways.

Direct contact between dendritic cells and bronchial epithelial cells inhibits T cell recall responses towards mite and pollen allergen extracts in vitro

Airway epithelial cells (AECs) form a polarized barrier along the respiratory tract. They are the first point of contact with airborne antigens and are able to instruct resident immune cells to mount appropriate immune responses by either soluble or contact-dependent mechanisms. We hypothesize that a healthy, polarized epithelial cell layer inhibits inflammatory responses towards allergens to uphold homeostasis. Using an in-vitro co-culture model of the airway epithelium, where a polarized cell layer of bronchial epithelial cells can interact with dendritic cells (DCs), we have investigated recall T cell responses in allergic patients sensitized to house dust mite, grass and birch pollen. Using allergen extract-loaded DCs to stimulate autologous allergen-specific T cell lines, we show that AEC-imprinted DCs inhibit T cell proliferation significantly of Bet v 1-specific T cell lines as well as decrease interleukin (IL)-5 and IL-13 production, whereas inhibition of Phl p 5-specific T cells varied between different donors. Stimulating autologous CD4(+) T cells from allergic patients with AEC-imprinted DCs also inhibited proliferation significantly and decreased production of both T helper type 1 (Th1) and Th2 cytokines upon rechallenge. The inhibitory effects of AECs' contact with DCs were absent when allergen extract-loaded DCs had been exposed only to AECs supernatants, but present after direct contact with AECs. We conclude that direct contact between DCs and AECs inhibits T cell recall responses towards birch, grass and house dust mite allergens in vitro, suggesting that AECs-DC contact in vivo constitute a key element in mucosal homeostasis in relation to allergic sensitisation.

Glucagon induces airway smooth muscle relaxation by nitric oxide and prostaglandin E₂

Glucagon is a hyperglycemic pancreatic hormone that has been shown to provide a beneficial effect against asthmatic bronchospasm. We investigated the role of this hormone on airway smooth muscle contraction and lung inflammation using both in vitro and in vivo approaches. The action of glucagon on mouse cholinergic tracheal contraction was studied in a conventional organ bath system, and its effect on airway obstruction was also investigated using the whole-body pletysmographic technique in mice. We also tested the effect of glucagon on lipopolysaccharide (LPS)-induced airway hyperreactivity (AHR) and inflammation. The expression of glucagon receptor (GcgR), CREB, phospho-CREB, nitric oxide synthase (NOS)-3, pNOS-3 and cyclooxygenase (COX)-1 was evaluated by western blot, while prostaglandin E₂ (PGE₂) and tumour necrosis factor-α were quantified by enzyme-linked immunoassay and ELISA respectively. Glucagon partially inhibited carbachol-induced tracheal contraction in a mechanism clearly sensitive to des-His1-[Glu9]-glucagon amide, a GcgR antagonist. Remarkably, GcgR was more expressed in the lung and trachea with intact epithelium than in the epithelium-denuded trachea. In addition, the glucagon-mediated impairment of carbachol-induced contraction was prevented by either removing epithelial cells or blocking NOS (L-NAME), COX (indomethacin) or COX-1 (SC-560). In contrast, inhibitors of either heme oxygenase or COX-2 were inactive. Intranasal instillation of glucagon inhibited methacholine-induced airway obstruction by a mechanism sensitive to pretreatment with L-NAME, indomethacin and SC-560. Glucagon induced CREB and NOS-3 phosphorylation and increased PGE₂ levels in the lung tissue without altering COX-1 expression. Glucagon also inhibited LPS-induced AHR and bronchoalveolar inflammation. These findings suggest that glucagon possesses airway-relaxing properties that are mediated by epithelium-NOS-3-NO- and COX-1-PGE₂-dependent mechanisms.

AcCystatin, an immunoregulatory molecule from Angiostrongylus cantonensis, ameliorates the asthmatic response in an aluminium hydroxide/ovalbumin-induced rat model of asthma

Epidemiological surveys have demonstrated that helminth infections are negatively related to atopic diseases, including asthma. Defining and characterising specific helminth molecules that have excellent immunomodulatory capacities as potential therapeutics for the treatment or prophylaxis of allergic manifestations are of great interest. AcCystatin, a cystatin protease inhibitor of Angiostrongylus cantonensis, is a homologue of other nematode cystatins with immunoregulatory properties. Here, we aim to determine the effects of AcCystatin on an ovalbumin/aluminium hydroxide (OVA/Al[OH]3)-induced rat model of asthma. Wistar rats were randomly divided into four groups, including a control group, an OVA/Al[OH]3-induced asthma group, a group receiving AcCystatin immunisation prior to OVA/Al[OH]3-induced asthma and a group receiving AcCystatin treatment after OVA/Al[OH]3-induced asthma. The numbers of eosinophils, basophils, neutrophils, lymphocytes and monocytes in the peripheral blood and of eosinophils in the bronchoalveolar lavage fluid (BALF) were counted for each animal. The expression levels of the cytokines interferon-γ, interleukin (IL) 4, IL-5, IL-6, IL-10, IL17A and tumour necrosis factor receptor-α in BALF, of OVA-specific immunoglobulin E in BALF and serum and of the chemokines eotaxin-1, eotaxin-2, eotaxin-3, MCP-1 and MCP-3 in lung tissue were measured. In addition, the degree of peribronchial and perivascular inflammation and the intensity of goblet cell metaplasia were qualitatively evaluated. The sensitised/challenged rats developed an extensive cell inflammatory response of the airways. AcCystatin administration significantly reduced the cellular infiltrate in the perivascular and peribronchial lung tissues and reduced both goblet mucous production and eosinophil infiltration. The rats that were treated with AcCystatin before or after sensitisation with OVA showed significant decreases in eotaxin-1, eotaxin-3 and MCP-1 expression in the lung tissue. The production of IL-4, IL-5, IL-6 and IL-17A and of OVA-specific IgE antibodies was also significantly reduced in AcCystatin-treated rats compared with untreated asthmatic rats. The AcCystatin treatment was associated with a significant increase in IL-10 levels. Our present findings provide the first demonstration that AcCystatin is an effective agent in the prevention and treatment of the airway inflammation associated with asthma.

Onset of diabetes modulates the airway smooth muscle reactivity of guinea pigs: role of epithelial mediators

BACKGROUND

Diabetes induces lung dysfunction, leading to alteration in the pulmonary functions. Our aim was to investigate whether the early stage of diabetes alters the epithelium-dependent bronchial responses and whether nitric oxide (NO), KATP channels and cyclooxygenase (COX) pathways contribute in this effect.

METHODS

Guinea pigs were treated with a single injection of streptozotocin (180 mg/kg, i.p.) for induction of diabetes. Airway conductivity was assessed by inhaled histamine, using a non-invasive body plethysmography. The contractile responses of tracheal rings induced by acetylcholine (ACh) and relaxant responses of precontracted rings, induced by isoproterenol (IP) were compared in the presence and absence of the epithelium. Effects of N(ω)-Nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), glybenclamide (a KATP channel inhibitor) and indomethacin (a COX inhibitor) were also assessed in diabetic guinea pigs.

RESULTS

Early stage diabetes did not alter the airway conductivity. ACh-induced bronchoconstriction in epithelium intact tracheal rings was not affected by the onset of diabetes, however a reduction in the increased ACh responses due to epithelium removal, to L-NAME or to indomethacin was observed. The relaxation response to IP was impaired in trachea from guinea pigs in which diabetes had just developed. Early diabetes significantly reduced the IP response to glybenclamide and to indomethacin.

CONCLUSION

Our results demonstrate that the early stage of diabetes, modulate the bronchial reactivity to both ACh and IP by disrupting the NO, KATP channels and COX pathways, without affecting the airway conductivity in guinea pigs.

The anti-asthma herbal medicine ASHMI acutely inhibits airway smooth muscle contraction via prostaglandin E2 activation of EP2/EP4 receptors

Our previous studies have shown that the anti-asthma traditional Chinese medicine herbal formula ASHMI (anti-asthma simplified herbal medicine intervention) inhibits acetylcholine-induced contractions of tracheal rings from ovalbumin-sensitized and naive mice in a β-adrenoceptor-independent manner. We sought to determine whether acute in vivo ASHMI administration inhibits airway hyperreactivity (AHR) in a murine model of allergic asthma and acetylcholine-induced tracheal ring constriction ex vivo and to elucidate the cellular mechanisms underlying these effects. Ovalbumin-sensitized mice received a single oral ASHMI dose 2 h before intravenous acetylcholine challenge. AHR was determined by invasive airway measurements. Myography was used to determine the effects of ASHMI on acetylcholine-induced constriction of tracheal rings from asthmatic mice with or without epithelial denudation. The effect of cyclooxygenase inhibition and EP2/EP4 receptor blockade on ASHMI attenuation of acetylcholine contractions was evaluated. Tracheal cAMP and PGE2 levels were measured by ELISA. A single acute oral dose of ASHMI dramatically reduced AHR in response to acetylcholine provocation in ovalbumin-sensitized mice (P < 0.001). In ex vivo experiments, ASHMI significantly and dose-dependently reduced tracheal ring constriction to acetylcholine (P < 0.05-0.001), which was epithelium independent and associated with elevated cAMP levels. This effect was abrogated by cyclooxygenase inhibition or EP2/EP4 receptor blockade. ASHMI also inhibited contraction to high K(+) (P < 0.001). ASHMI increased tracheal ring PGE2 release in response to acetylcholine or high K(+) (P < 0.05 for both). ASHMI produced direct and acute inhibition of AHR in vivo and blocked acetylcholine-induced tracheal ring constriction via the EP2/EP4 receptor pathway, identifying the mechanism by which ASHMI is an orally active bronchoprotective agent.

The thioredoxin system as a therapeutic target in human health and disease

The thioredoxin (Trx) system comprises Trx, truncated Trx (Trx-80), Trx reductase, and NADPH, besides a natural Trx inhibitor, the thioredoxin-interacting protein (TXNIP). This system is essential for maintaining the balance of the cellular redox status, and it is involved in the regulation of redox signaling. It is also pivotal for growth promotion, neuroprotection, inflammatory modulation, antiapoptosis, immune function, and atherosclerosis. As an ubiquitous and multifunctional protein, Trx is expressed in all forms of life, executing its function through its antioxidative, protein-reducing, and signal-transducing activities. In this review, the biological properties of the Trx system are highlighted, and its implications in several human diseases are discussed, including cardiovascular diseases, heart failure, stroke, inflammation, metabolic syndrome, neurodegenerative diseases, arthritis, and cancer. The last chapter addresses the emerging therapeutic approaches targeting the Trx system in human diseases.

Mangiferin prevents guinea pig tracheal contraction via activation of the nitric oxide-cyclic GMP pathway

Previous studies have described the antispasmodic effect of mangiferin, a natural glucoside xanthone (2-C-β-Dgluco-pyranosyl-1,3,6,7-tetrahydroxyxanthone) that is present in mango trees and other plants, but its mechanism of action remains unknown. The aim of this study was to examine the potential contribution of the nitric oxide-cyclic GMP pathway to the antispasmodic effect of mangiferin on isolated tracheal rings preparations. The functional effect of mangiferin on allergic and non-allergic contraction of guinea pig tracheal rings was assessed in conventional organ baths. Cultured tracheal rings were exposed to mangiferin or vehicle, and nitric oxide synthase (NOS) 3 and cyclic GMP (cGMP) levels were quantified using western blotting and enzyme immunoassays, respectively. Mangiferin (0.1–10 µM) inhibited tracheal contractions induced by distinct stimuli, such as allergen, histamine, 5-hydroxytryptamine or carbachol, in a concentration-dependent manner. Mangiferin also caused marked relaxation of tracheal rings that were precontracted by carbachol, suggesting that it has both anti-contraction and relaxant properties that are prevented by removing the epithelium. The effect of mangiferin was inhibited by the nitric oxide synthase inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME) (100 µM), and the soluble guanylate cyclase inhibitor, 1H-[1], [2], [4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µM), but not the adenylate cyclase inhibitor, 9-(tetrahydro-2-furyl)adenine (SQ22536) (100 µM). The antispasmodic effect of mangiferin was also sensitive to K⁺ channel blockers, such as tetraethylammonium (TEA), glibenclamide and apamin. Furthermore, mangiferin inhibited Ca²⁺-induced contractions in K⁺ (60 mM)-depolarised tracheal rings preparations. In addition, mangiferin increased NOS3 protein levels and cGMP intracellular levels in cultured tracheal rings. Finally, mangiferin-induced increase in cGMP levels was abrogated by co-incubation with either ODQ or L-NAME. These data suggest that the antispasmodic effect of mangiferin is mediated by epithelium-nitric oxide- and cGMP-dependent mechanisms.

Urothelial signaling

The urothelium, which lines the inner surface of the renal pelvis, the ureters, and the urinary bladder, not only forms a high-resistance barrier to ion, solute and water flux, and pathogens, but also functions as an integral part of a sensory web which receives, amplifies, and transmits information about its external milieu. Urothelial cells have the ability to sense changes in their extracellular environment, and respond to chemical, mechanical and thermal stimuli by releasing various factors such as ATP, nitric oxide, and acetylcholine. They express a variety of receptors and ion channels, including P2X3 purinergic receptors, nicotinic and muscarinic receptors, and TRP channels, which all have been implicated in urothelial-neuronal interactions, and involved in signals that via components in the underlying lamina propria, such as interstitial cells, can be amplified and conveyed to nerves, detrusor muscle cells, and ultimately the central nervous system. The specialized anatomy of the urothelium and underlying structures, and the possible communication mechanisms from urothelial cells to various cell types within the bladder wall are described. Changes in the urothelium/lamina propria ("mucosa") produced by different bladder disorders are discussed, as well as the mucosa as a target for therapeutic interventions.

Airway epithelium-derived relaxing factor: myth, reality, or naivety?

The presence of a healthy epithelium can moderate the contraction of the underlying airway smooth muscle. This is, in part, because epithelial cells generate inhibitory messages, whether diffusible substances, electrophysiological signals, or both. The epithelium-dependent inhibitory effect can be tonic (basal), synergistic, or evoked. Rather than a unique epithelium-derived relaxing factor (EpDRF), several known endogenous bronchoactive mediators, including nitric oxide and prostaglandin E2, contribute. The early concept that EpDRF diffuses all the way through the subepithelial layers to directly relax the airway smooth muscle appears unlikely. It is more plausible that the epithelial cells release true messenger molecules, which alter the production of endogenous substances (nitric oxide and/or metabolites of arachidonic acid) by the subepithelial layers. These substances then diffuse to the airway smooth muscle cells, conveying epithelium dependency.

The role of alveolar epithelium in radiation-induced lung injury

Pneumonitis and fibrosis are major lung complications of irradiating thoracic malignancies. In the current study, we determined the effect of thoracic irradiation on the lungs of FVB/N mice. Survival data showed a dose-dependent increase in morbidity following thoracic irradiation with single (11–13 Gy) and fractionated doses (24–36 Gy) of ¹³⁷Cs γ-rays. Histological examination showed a thickening of vessel walls, accumulation of inflammatory cells, collagen deposition, and regional fibrosis in the lungs 14 weeks after a single 12 Gy dose and a fractionated 30 Gy dose; this damage was also seen 5 months after a fractionated 24 Gy dose. After both single and fractionated doses, i] aquaporin-5 was markedly decreased, ii] E-cadherin was reduced and iii] prosurfactant Protein C (pro-SP-c), the number of pro-SP-c⁺ cells and vimentin expression were increased in the lungs. Immunofluorescence analysis revealed co-localization of pro-SP-c and α-smooth muscle actin in the alveoli after a single dose of 12 Gy. These data suggest that, i] the FVB/N mouse strain is sensitive to thoracic radiation ii] aquaporin-5, E-cadherin, and pro-SP-c may serve as sensitive indicators of radiation-induced lung injury; and iii] the epithelial-to-mesenchymal transition may play an important role in the development of radiation-induced lung fibrosis.

Activation of endothelial and epithelial K(Ca) 2.3 calcium-activated potassium channels by NS309 relaxes human small pulmonary arteries and bronchioles

BACKGROUND AND PURPOSE

Small (K(Ca) 2) and intermediate (K(Ca) 3.1) conductance calcium-activated potassium channels (K(Ca) ) may contribute to both epithelium- and endothelium-dependent relaxations, but this has not been established in human pulmonary arteries and bronchioles. Therefore, we investigated the expression of K(Ca) 2.3 and K(Ca) 3.1 channels, and hypothesized that activation of these channels would produce relaxation of human bronchioles and pulmonary arteries.

EXPERIMENTAL APPROACH

Channel expression and functional studies were conducted in human isolated small pulmonary arteries and bronchioles. K(Ca) 2 and K(Ca) 3.1 currents were examined in human small airways epithelial (HSAEpi) cells by whole-cell patch clamp techniques.

RESULTS

While K(Ca) 2.3 expression was similar, K(Ca) 3.1 protein was more highly expressed in pulmonary arteries than bronchioles. Immunoreactive K(Ca) 2.3 and K(Ca) 3.1 proteins were found in both endothelium and epithelium. K(Ca) currents were present in HSAEpi cells and sensitive to the K(Ca) 2.3 blocker UCL1684 and the K(Ca) 3.1 blocker TRAM-34. In pulmonary arteries contracted by U46619 and in bronchioles contracted by histamine, the K(Ca) 2.3/ K(Ca) 3.1 activator, NS309, induced concentration-dependent relaxations. NS309 was equally potent in relaxing pulmonary arteries, but less potent in bronchioles, than salbutamol. NS309 relaxations were blocked by the K(Ca) 2 channel blocker apamin, while the K(Ca) 3.1 channel blocker, charybdotoxin failed to reduce relaxation to NS309 (0.01-1 µM).

CONCLUSIONS AND IMPLICATIONS

K(Ca) 2.3 and K(Ca) 3.1 channels are expressed in the endothelium of human pulmonary arteries and epithelium of bronchioles. K(Ca) 2.3 channels contributed to endo- and epithelium-dependent relaxations suggesting that these channels are potential targets for treatment of pulmonary hypertension and chronic obstructive pulmonary disease.

From urothelial signalling to experiencing a sensation related to the urinary bladder

The mechanisms underlying bladder sensation and the way we experience sensations during normal voiding and in pathology is complex and not well understood. During storage and emptying, mechanical changes occurring in number of cell types within the bladder wall (i.e. the uroepithelium and bladder afferents) can have a major influence on our sensory systems. In this review, we discuss bladder sensation with a focus on coding events in the periphery.

Flow cytometric isolation of primary murine type II alveolar epithelial cells for functional and molecular studies

Throughout the last years, the contribution of alveolar type II epithelial cells (AECII) to various aspects of immune regulation in the lung has been increasingly recognized. AECII have been shown to participate in cytokine production in inflamed airways and to even act as antigen-presenting cells in both infection and T-cell mediated autoimmunity (1-8). Therefore, they are especially interesting also in clinical contexts such as airway hyper-reactivity to foreign and self-antigens as well as infections that directly or indirectly target AECII. However, our understanding of the detailed immunologic functions served by alveolar type II epithelial cells in the healthy lung as well as in inflammation remains fragmentary. Many studies regarding AECII function are performed using mouse or human alveolar epithelial cell lines (9-12). Working with cell lines certainly offers a range of benefits, such as the availability of large numbers of cells for extensive analyses. However, we believe the use of primary murine AECII allows a better understanding of the role of this cell type in complex processes like infection or autoimmune inflammation. Primary murine AECII can be isolated directly from animals suffering from such respiratory conditions, meaning they have been subject to all additional extrinsic factors playing a role in the analyzed setting. As an example, viable AECII can be isolated from mice intranasally infected with influenza A virus, which primarily targets these cells for replication (13). Importantly, through ex vivo infection of AECII isolated from healthy mice, studies of the cellular responses mounted upon infection can be further extended. Our protocol for the isolation of primary murine AECII is based on enzymatic digestion of the mouse lung followed by labeling of the resulting cell suspension with antibodies specific for CD11c, CD11b, F4/80, CD19, CD45 and CD16/CD32. Granular AECII are then identified as the unlabeled and sideward scatter high (SSC(high)) cell population and are separated by fluorescence activated cell sorting (3). In comparison to alternative methods of isolating primary epithelial cells from mouse lungs, our protocol for flow cytometric isolation of AECII by negative selection yields untouched, highly viable and pure AECII in relatively short time. Additionally, and in contrast to conventional methods of isolation by panning and depletion of lymphocytes via binding of antibody-coupled magnetic beads (14, 15), flow cytometric cell-sorting allows discrimination by means of cell size and granularity. Given that instrumentation for flow cytometric cell sorting is available, the described procedure can be applied at relatively low costs. Next to standard antibodies and enzymes for lung disintegration, no additional reagents such as magnetic beads are required. The isolated cells are suitable for a wide range of functional and molecular studies, which include in vitro culture and T-cell stimulation assays as well as transcriptome, proteome or secretome analyses (3, 4).

Nervous network for lower urinary tract function

Traditionally, sensory signaling in the urinary bladder has been largely attributed to direct activation of bladder afferents. There is substantive evidence that sensory systems can be influenced by non-neuronal cells, such as the urothelium, which are able to respond to various types of stimuli that can include physiological, psychological and disease-related factors. The corresponding release of chemical mediators (through activation of a number of receptors/ion channels) can initiate signaling mechanisms between and within urothelial cells, as well as other cell types within the bladder wall including bladder nerves. However, the mechanisms underlying how various cell types in the bladder wall respond to normal filling and emptying, and are challenged by a variety of stressors (physical and chemical) are still not well understood. Alterations or defects in signaling mechanisms are likely to contribute to the pathophysiology of bladder disease with symptoms including urinary urgency, increased voiding frequency and pain. This review will discuss some of the components involved in control of lower urinary tract function, with an emphasis on the sensor and transducer roles of the urothelium.

Enhancement of methacholine-evoked tracheal contraction induced by bacterial lipopolysaccharides depends on epithelium and tumor necrosis factor

Inhaled bacterial lipopolysaccharides (LPSs) induce an acute tumour necrosis factor-alpha (TNF-α-) dependent inflammatory response in the murine airways mediated by Toll-like receptor 4 (TLR4) via the myeloid differentiation MyD88 adaptor protein pathway. However, the contractile response of the bronchial smooth muscle and the role of endogenous TNFα in this process have been elusive. We determined the in vivo respiratory pattern of C57BL/6 mice after intranasal LPS administration with or without the presence of increasing doses of methacholine (MCh). We found that LPS administration altered the basal and MCh-evoked respiratory pattern that peaked at 90 min and decreased thereafter in the next 48 h, reaching basal levels 7 days later. We investigated in controlled ex vivo condition the isometric contraction of isolated tracheal rings in response to MCh cholinergic stimulation. We observed that preincubation of the tracheal rings with LPS for 90 min enhanced the subsequent MCh-induced contractile response (hyperreactivity), which was prevented by prior neutralization of TNFα with a specific antibody. Furthermore, hyperreactivity induced by LPS depended on an intact epithelium, whereas hyperreactivity induced by TNFα was well maintained in the absence of epithelium. Finally, the enhanced contractile response to MCh induced by LPS when compared with control mice was not observed in tracheal rings from TLR4- or TNF- or TNF-receptor-deficient mice. We conclude that bacterial endotoxin-mediated hyperreactivity of isolated tracheal rings to MCh depends upon TLR4 integrity that signals the activation of epithelium, which release endogenous TNFα.

Carbon dioxide enhances substance P-induced epithelium-dependent bronchial smooth muscle relaxation in Sprague-Dawley rats

Hypocapnia and hypercapnia constrict and relax airway smooth muscle, respectively, through pH- and calcium (Ca(2+))-mediated mechanisms. In this study we explore a potential role for the airway epithelium in these responses to carbon dioxide (CO(2)). Contractile and relaxant responses of isolated rat bronchial rings were measured under hypocapnic, eucapnic, and hypercapnic conditions. Substance P was added to methacholine precontracted bronchial rings with and without epithelium. The role of Ca(2+) was assessed using Ca(2+)-free solutions and a Ca(2+) channel blocker, nifedipine. The effects of pH were assessed in solutions with HEPES buffer. Hypocapnic challenge increased the organ bath's pH and increased bronchial smooth muscle resting tension. This effect was abolished with HEPES buffer and partially inhibited by nifedipine. Hypocapnic conditions suppressed substance P-induced epithelium-dependent relaxation, whereas hypercapnia augmented the response. The epithelial hypocapnic effect was pH dependent, whereas the hypercapnic effect was pH independent. CO(2) had no effect on the epithelial independent smooth muscle agonists methacholine and isoproterenol. In conclusion our data indicate that, in addition to the effects of pH and Ca(2+), CO(2) affects airway smooth muscle by a pH-independent, epithelium-mediated mechanism. These findings could potentially lead to new treatments for asthma involving CO(2)-sensing receptors in the airways.

Local small airway epithelial injury induces global smooth muscle contraction and airway constriction

Small airway epithelial cells form a continuous sheet lining the conducting airways, which serves many functions including a physical barrier to protect the underlying tissue. In asthma, injury to epithelial cells can occur during bronchoconstriction, which may exacerbate airway hyperreactivity. To investigate the role of epithelial cell rupture in airway constriction, laser ablation was used to precisely rupture individual airway epithelial cells of small airways (<300-μm diameter) in rat lung slices (∼250-μm thick). Laser ablation of single epithelial cells using a femtosecond laser reproducibly induced airway contraction to ∼70% of the original cross-sectional area within several seconds, and the contraction lasted for up to 40 s. The airway constriction could be mimicked by mechanical rupture of a single epithelial cell using a sharp glass micropipette but not with a blunt glass pipette. These results suggest that soluble mediators released from the wounded epithelial cell induce global airway contraction. To confirm this hypothesis, the lysate of primary human small airway epithelial cells stimulated a similar airway contraction. Laser ablation of single epithelial cells triggered a single instantaneous Ca(2+) wave in the epithelium, and multiple Ca(2+) waves in smooth muscle cells, which were delayed by several seconds. Removal of extracellular Ca(2+) or decreasing intracellular Ca(2+) both blocked laser-induced airway contraction. We conclude that local epithelial cell rupture induces rapid and global airway constriction through release of soluble mediators and subsequent Ca(2+)-dependent smooth muscle shortening.

Tracheal relaxation of five Ivorian anti-asthmatic plants: role of epithelium and K⁺ channels in the effect of the aqueous-alcoholic extract of Dichrostachys cinerea root bark

ETHNOPHARMACOLOGICAL RELEVANCE

Leaves of Boerhavia diffusa (Nyctaginaceae), Baphia nitida, Cassia occidentalis, Desmodium adscendens (Fabaceae), and root bark of Dichrostachys cinerea (Fabaceae) are used in Ivory Coast for the treatment of asthma. The aim of this study was to evaluate the potential airway relaxant activity of different extracts of these plants.

MATERIALS AND METHODS

Extracts of different polarities (H(2)O, EtOH/H(2)O, MeOH and CH(2)Cl(2)) were obtained from these five plants. Their ex vivo relaxant activity was tested in mice isolated trachea precontracted with carbachol (1 μM).

RESULTS

Cumulative concentrations of most extracts induced moderate to strong relaxation, the methanolic extracts being the most potent and the polar extracts the most active at the concentrations used, supporting the traditional use of these five plants as anti-asthmatic remedies. We further investigated the molecular and cellular mechanisms of the mouse trachea relaxant effect of the aqueous-alcoholic extract of Dichrostachys cinerea root bark, the most potent extract. Its effect was not modified in the presence of β-adrenoceptor antagonists (propranolol or ICI 118,551) or a PKA inhibitor (H89). By contrast, it was decreased after depolarization-induced precontraction (with 80 mM KCl), in the presence of some K(+) channels blockers [4-aminopyridine as voltage-dependent K(+) (K(v)) channel blocker and tetraethylammonium chloride as large conductance Ca(2+)-activated K(+) (BK(Ca)) channel blocker, but not with glibenclamide, an ATP-sensitive K(+) (K(ATP)) channel blocker] or after epithelium removal.

CONCLUSIONS

The mouse tracheal relaxant effect of Dichrostachys cinerea EtOH/H(2)O extract was independent of β(2)-adrenoceptors activation and cAMP/PKA pathway, but dependent on epithelium and K(+) channels, namely K(v) and BK(Ca) channels. Further investigation will be required to identify the component(s) responsible for this airways relaxant activity.

Apical localization of zinc transporter ZnT4 in human airway epithelial cells and its loss in a murine model of allergic airway inflammation

The apical cytoplasm of airway epithelium (AE) contains abundant labile zinc (Zn) ions that are involved in the protection of AE from oxidants and inhaled noxious substances. A major question is how dietary Zn traffics to this compartment. In rat airways, in vivo selenite autometallographic (Se-AMG)-electron microscopy revealed labile Zn-selenium nanocrystals in structures resembling secretory vesicles in the apical cytoplasm. This observation was consistent with the starry-sky Zinquin fluorescence staining of labile Zn ions confined to the same region. The vesicular Zn transporter ZnT4 was likewise prominent in both the apical and basal parts of the epithelium both in rodent and human AE, although the apical pools were more obvious. Expression of ZnT4 mRNA was unaffected by changes in the extracellular Zn concentration. However, levels increased 3-fold during growth of cells in air liquid interface cultures and decreased sharply in the presence of retinoic acid. When comparing nasal versus bronchial human AE cells, there were significant positive correlations between levels of ZnT4 from the same subject, suggesting that nasal brushings may allow monitoring of airway Zn transporter expression. Finally, there were marked losses of both basally-located ZnT4 protein and labile Zn in the bronchial epithelium of mice with allergic airway inflammation. This study is the first to describe co-localization of zinc vesicles with the specific zinc transporter ZnT4 in airway epithelium and loss of ZnT4 protein in inflamed airways. Direct evidence that ZnT4 regulates Zn levels in the epithelium still needs to be provided. We speculate that ZnT4 is an important regulator of zinc ion accumulation in secretory apical vesicles and that the loss of labile Zn and ZnT4 in airway inflammation contributes to AE vulnerability in diseases such as asthma.

Regulation of smooth muscle contraction by the epithelium: role of prostaglandins

As an analog to the endothelium situated next to the vascular smooth muscle, the epithelium is emerging as an important regulator of smooth muscle contraction in many vital organs/tissues by interacting with other cell types and releasing epithelium-derived factors, among which prostaglandins have been demonstrated to play a versatile role in governing smooth muscle contraction essential to the physiological and pathophysiological processes in a wide range of organ systems.

Response to oyster mushroom (Pleurotus ostreatus) extract by sensitized and nonsensitized guinea pig trachea

Occupational exposure to oyster mushroom (Pleurotus ostreatus) has been associated with obstructive lung disease. Previously, we studied an extract of oyster mushroom (OME) and determined that it causes dose-dependent contractions of nonsensitized guinea pig trachea (GPT). We extend these studies to the investigation of sensitized tissue. In the present study 24 animals were sensitized using ovalbumin (OA) and subsequently challenged with an aerosol of 2.5% OA. A control group of 12 nonsensitized GPs was also studied. Tracheas were removed and were divided into rings in which the epithelium was retained (EP+) or removed (EP-). Dose-related contractions of sensitized and nonsensitized GPTs were elicited with OME. In nonsensitized animals the EP+ GPTs demonstrated a significantly greater response to OME (100-1000 μl) than did the EP- GPTs (p < 0.01). By contrast, in sensitized GPTs with and without epithelium there was no difference to challenge with OME. Finally, sensitized GPTs with and without epithelium and nonsensitized GPTs with epithelium responded similarly to challenge with OME. These findings suggest that in nonsensitized animals there is an enhancement of contractile response to OME which is in part mediated by the GPT epithelium. In sensitized animals with or without epithelium, the level of bronchoconstrictor response is similar to that of the nonsensitized animals with epithelium, suggesting an enhanced constrictor response independent of epithelium in the sensitized animals.

Mechanisms of relaxant activity of the nitric oxide-independent soluble guanylyl cyclase stimulator BAY 41-2272 in rat tracheal smooth muscle

The soluble guanylyl cyclase is expressed in airway smooth muscle, and agents that stimulate this enzyme activity cause airway smooth muscle relaxation and bronchodilation. The compound 5-Cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine (BAY 41-2272) is a potent nitric oxide (NO)-independent soluble guanylyl cyclase stimulator, but little is known about its effects in airway smooth muscle. Therefore, this study aimed to investigate the mechanisms underlying the relaxations of rat tracheal smooth muscle induced by BAY 41-2272. Tracheal rings were mounted in 10-ml organ baths for isometric force recording. BAY 41-2272 concentration-dependently relaxed carbachol-precontracted tracheal rings (pEC(50)=6.68+/-0.14). Prior incubation with the NO synthesis inhibitor l-NAME (100 microM) or the soluble guanylyl cyclase inhibitor ODQ (10 microM) caused significant rightward shifts in the concentration-response curves to BAY 41-2272. Sodium nitroprusside caused concentration-dependent relaxations, which were greatly potentiated by BAY 41-2272 and completely inhibited by ODQ. In addition, BAY 41-2272 shifted to the right the tracheal contractile responses to either carbachol (0.01-1 microM) or electrical field stimulation (EFS, 1-32 Hz). BAY 41-2272 (1 microM) also caused a marked rightward shift and decreased the maximal contractile responses to extracellular CaCl2, and such effect was not modified by pretreatment with ODQ. In addition, BAY 41-2272 (up to 1 microM) significantly increased the cGMP levels, and that was abolished by ODQ. Our results indicate that BAY 41-2272 causes cGMP-dependent rat tracheal smooth muscle relaxations in a synergistic fashion with exogenous NO. BAY 41-2272 has also an additional mechanism independently of soluble guanylyl cyclase activation possibly involving Ca(2+) entry blockade.

Identification and characterization of β-adrenergic receptors in isolated primary equine tracheal epithelial cells

Responses and functions of airway epithelial cells are stimulated by β₂-agonists via the β₂-adrenergic receptors (β₂-ARs)-G(s)-protein-cAMP-system, thus, affecting airway inflammation such as in asthma and equine recurrent airway obstruction (RAO). Though horses can be used as large animal model for human asthma, evaluation of the expression and functions of the β-AR system in primary equine airway epithelial cells has not been yet carried out. Thus, for the first time, we determined the β-AR density and subtype distribution by [¹²⁵I]-iodocyanopindolol (ICYP) binding, examined β-AR function by cAMP assay as well as their expression by western blot analysis and immunocytochemical staining in primary equine tracheal epithelial cells (ETEC). Cells were collected from 19 horses and cultured subsequently. The specific ICYP binding was saturable and of high affinity: in freshly isolated cells the receptor density (B(max)) and ICYP affinity (K(D)) for β-ARs were 12727 ± 883 binding sites/cell and 31.78 ± 6.57 pM, respectively, and in cultured ETEC 3730 ± 212 binding sites/cell and 15.26 ± 3.37 pM, respectively. The β-AR subtype assessed by β₁-selective (CGP 20712A) and β₂-selective (ICI 118.551) adrenergic receptor antagonists demonstrated that the β₂-AR subtype predominated (>95%) in both cell populations (p < 0.001). The β-AR agonists increased cAMP formation with a rank order of potency: isoproterenol > epinephrine > norepinephrine. ICI 118.551 (100 nM) significantly blocked (p < 0.05) isoproterenol-induced cAMP accumulation but not CGP 20712A (300 nM). Western blot analyses and immunocytochemical staining further indicated the expression of the β(2)-AR subtype in both cell preparations. Our data indicate that in acutely dissociated and primary cultured ETEC the β(2)-AR-AC system is expressed, but varies considerably between the two preparations.

Mechanisms underlying epithelium-dependent relaxation in rat bronchioles: analogy to EDHF-type relaxation in rat pulmonary arteries

This study investigated the mechanisms underlying epithelium-derived hyperpolarizing factor (EpDHF)-type relaxation in rat bronchioles. Immunohistochemistry was performed, and rat bronchioles and pulmonary arteries were mounted in microvascular myographs for functional studies. An opener of small (SKCa) and intermediate (IKCa)-conductance calcium-activated potassium channels, NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime) was used to induce EpDHF-type relaxation. IKCa and SKCa3 positive immunoreactions were observed mainly in the epithelium and endothelium of bronchioles and arteries, respectively. In 5-hydroxytryptamine (1 μM)-contracted bronchioles (828 ± 20 μm, n = 84) and U46619 (0.03 μM)-contracted arteries (720 ± 24 μm, n = 68), NS309 (0.001–10 μM) induced concentration-dependent relaxations that were reduced by epithelium/endothelium removal and by blocking IKCa channels with charybdotoxin and in bronchioles also by blocking SKCa channels with apamin. Inhibition of cyclooxygenase, nitric oxide synthase, and cytochrome 2C isoenzymes, or blockade of large (BKCa)-conductance calcium-activated potassium channels with iberiotoxin, failed to reduce NS309 relaxation. In contrast to the pulmonary arteries, relaxations to a β2-adrenoceptor agonist, salbutamol, were reduced in bronchioles by removing the epithelium or blocking IKCa and/or SKCa channels. Extracellular K+ (2–20 mM) induced relaxation in both bronchioles and arteries. An inhibitor of Na+-K+-ATPase, ouabain, abolished relaxations to NS309, salbutamol, and K+. These results suggest that IKCa and SKCa3 channels are located in the epithelium of bronchioles and endothelium of pulmonary arteries. Analog to the endothelium-derived hyperpolarizing factor (EDHF)-type relaxation in pulmonary arteries, these channels may be involved in EpDHF-type relaxation of bronchioles caused by epithelial K+ efflux followed by activation of Na+-K+-ATPase in the underlying smooth muscle layer.

Inhibitory effect of quercetin on rat trachea contractility in vitro

Objectives

The effect of quercetin, a naturally occurring flavonoid traditionally used to treat airway diseases such as bronchial asthma, on the contractile response elicited by electrical field stimulation or carbachol in rat isolated trachea was investigated.

Methods

Isolated tracheal tissue was subjected to contractions by an electrical field stimulation of 5 Hz for 30 s, 400 mA, and the responses in the presence of cumulative concentrations of quercetin (10−6−3 × 10−4 M) were observed. The effect of quercetin was also evaluated after administration of phentolamine plus propranolol (to block α- and β-adrenergic receptors), NG-nitro-L-arginine methyl ester (to block nitric oxide synthesis), capsaicin (to desensitise sensory C fibres), α-chymotrypsin (a proteolytic enzyme that rapidly degrades vasoactive intestinal peptide), SR140333 and SR48968 (tackykinin NK1 and NK2 receptor antagonists, respectively).

Key findings

Quercetin produced a concentration-dependent inhibition of contractions induced by both carbachol and electrical field stimulation. However, quercetin was more active in inhibiting the contractions produced by electrical field stimulation than those induced by carbachol, suggesting a presynaptic site of action (in addition to a postsynaptic effect, as revealed by the inhibitory action of quercetin on carbachol-induced contractions). The inhibitory effect of quercetin on contractions induced by electrical field stimulation was unaffected by phentolamine plus propranolol, SR 140333 and SR 48968, capsaicin treatment or by the proteolytic enzyme α-chymotrypsin. In contrast, the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester significantly reduced the inhibitory effect of quercetin on contractions induced by electrical field stimulation.

Conclusions

Quercetin inhibits rat tracheal contractility through a presynaptic (involving nitric oxide) and a postsynaptic site of action.

Chronic inflammation and asthma

Allergic asthma is a complex and chronic inflammatory disorder which is associated with airway hyper-responsiveness and tissue remodelling of the airway structure. Although originally thought to be a Th2-driven inflammatory response to inhaled innocuous allergen, the immune response in asthma is now considered highly heterogeneous. There are now various in vivo systems which have been designed to examine the pathways leading to the development of this chronic immune response and reflect, in part this heterogeneity. Furthermore, the emergence of endogenous immunoregulatory pathways and active pro-resolving mediators hold great potential for future therapeutic intervention. In this review, the key cellular and molecular mediators relating to chronic allergic airway disease are discussed, as well as emerging players in the regulation of chronic allergic inflammation.

Modulatory role of endogenous androgens on airway smooth muscle tone in isolated guinea-pig and bovine trachea; involvement of beta2-adrenoceptors, the polyamine system and external calcium

Androgens relax several smooth muscles, including the airways. They also contract ileum and myocardium via nongenomic mechanisms. To find out whether androgens modulate airway smooth muscles in different species and further assess their mechanism of action, regarding the role of beta-adrenoceptors, polyamines and extracellular Ca(2+), and the modulation of contraction, 5 alpha-dihydrotestosterone, testosterone and 5 beta-dihydrotestosterone were used. A preliminary study was performed to evaluate the effect of 5 alpha-dihydrotestosterone, a non-aromatisable derivate of testosterone, in isolated guinea-pig trachea and a more exhaustive characterisation was followed in bovine trachea, to also characterise the effect of testosterone and 5 beta-dihydrotestosterone. The androgens elicited a nongenomic epithelium-independent relaxation of the trachea which had been precontracted. In the bovine trachea, the order of potency was: testosterone>5 alpha-dihydrotestosterone=5 beta-dihydrotestosterone. This effect was inversely proportional to the magnitude of carbachol-raised tone and was independent of beta(2)-adrenoceptors, since the beta-blockers, propranolol and ICI-118,551, and beta(2)-adrenoceptor desensitisation did not modify 5 alpha-dihydrotestosterone-elicited relaxation. 5 alpha-Dihydrotestosterone was unable to displace the radiolabel, [(3)H]dihydroalprenolol, from these receptors in the binding assay. Polyamine synthesis was not involved in this androgen effect, since an ornithine decarboxylase inhibitor, alpha-difluoromethylornithine, was ineffective. The androgens were more effective relaxing bovine trachea precontracted by KCl (80 mM), suggesting a calcium entry blockade, as reported for several smooth muscles. This mechanism might be involved in the observed 5 alpha-dihydrotestosterone facilitation of salbutamol-relaxation. Androgens facilitated carbachol-elicited contraction independently of polyamine synthesis, contrary to what has been reported in the ileum. Therefore, androgens modulate tracheal smooth muscle tone which might be of importance in the regulation of airway reactivity.

Downregulation of protease-activated receptor-1 in human lung fibroblasts is specifically mediated by the prostaglandin E receptor EP2 through cAMP elevation and protein kinase A

Many cellular functions of lung fibroblasts are controlled by protease-activated receptors (PARs). In fibrotic diseases, PAR-1 plays a major role in controlling fibroproliferative and inflammatory responses. Therefore, in these diseases, regulation of PAR-1 expression plays an important role. Using the selective prostaglandin EP2 receptor agonist butaprost and cAMP-elevating agents, we show here that prostaglandin (PG)E(2), via the prostanoid receptor EP2 and subsequent cAMP elevation, downregulates mRNA and protein levels of PAR-1 in human lung fibroblasts. Under these conditions, the functional response of PAR-1 in fibroblasts is reduced. These effects are specific for PGE(2). Activation of other receptors coupled to cAMP elevation, such as beta-adrenergic and adenosine receptors, does not reproduce the effects of PGE(2). PGE(2)-mediated downregulation of PAR-1 depends mainly on protein kinase A activity, but does not depend on another cAMP effector, the exchange protein activated by cAMP. PGE(2)-induced reduction of PAR-1 level is not due to a decrease of PAR-1 mRNA stability, but rather to transcriptional regulation. The present results provide further insights into the therapeutic potential of PGE(2) to specifically control fibroblast function in fibrotic diseases.

Interactions between epithelial cells and dendritic cells in airway immune responses: lessons from allergic airway disease

Micro-organisms constantly invade the human body and may form a threat to our health. Traditionally, concepts of defence mechanisms have included a protective outer layer of epithelia and a vigilant immune system searching for areas where the integrity of the outer layer may be compromised. Instead of considering these elements as two independent mechanisms, we should be treating them as a single integrated system. This review will present and discuss the role of local immune-competent cells and local epithelia in the recognition of potential pathogens and how the interaction between the two components may affect the initiation of the airway immune response. A concept emerges where airway mucosal dendritic cells act as integrators of both immunostimulatory and immunosuppressive signals that act within actively-involved mucosal tissue.

Cell types involved in allergic asthma and their use in in vitro models to assess respiratory sensitization

This review first describes the mechanism and cell types involved in allergic asthma, which is a complex clinical disease characterized by airway obstruction, airway inflammation and airway hyperresponsiveness to a variety of stimuli. The development of allergic asthma exists of three phases, namely the induction phase, the early-phase asthmatic reaction (EAR) and the late-phase asthmatic reaction (LAR). In the induction phase, antigen-presenting cells play a major role. Most important cells in the EAR are mast cells, and during the LAR, various cell types, such as eosinophils, neutrophils, T cells, macrophages, dendritic cells (DCs), and cells that endow structure are involved. In occupational asthma, this immunological mechanism is involved in 90% of the cases. The second part of this review gives an overview of in vitro models to assess the hazardous potential of high- and low-molecular weight chemicals on the respiratory system. In order to develop a good in vitro model for respiratory allergy, the choice of appropriate cell types is important. Epithelial cells, macrophages and DCs are currently the most used models in this field of research.

Isolation and culture of primary equine tracheal epithelial cells

Culture of airway epithelial cells is a useful model to investigate physiology of airway epithelia and airway disease mechanisms. In vitro models of airway epithelial cells are established for various species. However, earlier published method for isolation and culture of equine tracheal epithelial cells requires significant improvements. In this report, the development of a procedure for efficient isolation, characterization, culture, and passage of primary equine tracheal epithelial cells are described. Epithelial cells were isolated from adult equine trachea by exposing and stripping the mucosal epithelium from the adjacent connective tissue and smooth muscle. The tissue was minced and dissociated enzymatically using 0.25% trypsin-ethylenediaminetetraacetic acid (EDTA) solution for 2 h at 37 degrees C. Cells were collected by sieving and centrifugation, and contaminating fibroblasts were removed by differential adhesion. This procedure resulted in a typical yield of 1 x 10(7) cytokeratin-positive epithelial cells per gram tracheal lining tissue. Viability was 95% by trypan blue exclusion and isolates contained approximately 94% cytokeratin-positive cells of epithelial origin. Cells seeded at a density of 6.9 x 10(4) cells/cm2 in serum-free airway epithelial cell growth medium formed monolayers near confluency within a week. Confluent cells were dissociated using dispase II and first passages (P1) and second passages (P2) were successfully established in serum-free medium. Collagen coating of tissue culture flask was not required for cell adhesion, and cultures could be maintained at the level of P2 over 30 d. In the present study, we could establish a high-yield protocol for isolation and culture of equine tracheal epithelial cells that can serve for in vitro/ex vivo studies on the (patho-)physiology of equine airway disease as well as pharmacological and toxicological targets relevant to airway diseases.

Suppression of Gadd45 alleviates the G2/M blockage and the enhanced phosphorylation of p53 and p38 in zinc supplemented normal human bronchial epithelial cells

An adequate zinc status is essential for optimal cellular functions and growth. Yet, excessive zinc supplementation can be cytotoxic and can impair cell growth. Gadd45 plays a vital role as cellular stress sensor in the modulation of cell signal transduction in response to stress. The present study was designed to determine the influence of zinc status on Gadd45 expression and cell cycle progression in zinc deficient and supplemented normal human bronchial epithelial (NHBE) cells, and to decipher the molecular mechanism(s) exerted by the suppression of Gadd45 expression on cell growth and cell cycle progression in this cell type. Cells were cultured for one passage in different concentration of zinc: <0.4 muM (ZD) as severe zinc deficient; 4 muM as normal zinc level in culture medium; 16 microM (ZA) as normal human plasma zinc level; and 32 muM (ZS) as the high end of plasma zinc attainable by oral supplementation. Inhibition of cell growth, upregulation of Gadd45 mRNA and protein expression, and blockage of G2/M cell cycle progression were observed in ZS cells. In contrast, little or no changes in these parameters were seen in ZD cells. The siRNA-mediated knocking down of Gadd45 was found to relieve G2/M blockage in ZS cells, which indicated that the blockage was Gadd45 dependent. Moreover, the enhanced phosphorylation of p38 and p53 (ser15) in ZS cells was normalized after suppression of Gadd45 by siRNA, implicating that the enhanced phosphorylation of these proteins was Gadd45 dependent. Thus, we demonstrated for the first time that an elevated zinc status modulated signal transduction to produce a delay at G2/M during cell cycle progression in NHBE cells.

Prostaglandin-induced activation of nociceptive neurons via direct interaction with transient receptor potential A1 (TRPA1)

Inflammation contributes to pain hypersensitivity through multiple mechanisms. Among the most well characterized of these is the sensitization of primary nociceptive neurons by arachidonic acid metabolites such as prostaglandins through G protein-coupled receptors. However, in light of the recent discovery that the nociceptor-specific ion channel transient receptor potential A1 (TRPA1) can be activated by exogenous electrophilic irritants through direct covalent modification, we reasoned that electrophilic carbon-containing A- and J-series prostaglandins, metabolites of prostaglandins (PG) E(2) and D(2), respectively, would excite nociceptive neurons through direct activation of TRPA1. Consistent with this prediction, the PGD(2) metabolite 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)) activated heterologously expressed human TRPA1 (hTRPA1-HEK), as well as a subset of chemosensitive mouse trigeminal neurons. The effects of 15dPGJ(2) on neurons were blocked by both the nonselective TRP channel blocker ruthenium red and the TRPA1 inhibitor (HC-030031), but unaffected by the TRPV1 blocker iodo-resiniferatoxin. In whole-cell patch-clamp studies on hTRPA1-HEK cells, 15dPGJ(2) evoked currents similar to equimolar allyl isothiocyanate (AITC) in the nominal absence of calcium, suggesting a direct mechanism of activation. Consistent with the hypothesis that TRPA1 activation required reactive electrophilic moieties, A- and J-series prostaglandins, and the isoprostane 8-iso-prostaglandin A(2)-evoked calcium influx in hTRPA1-HEK cells with similar potency and efficacy. It is noteworthy that this effect was not mimicked by their nonelectrophilic precursors, PGE(2) and PGD(2), or PGB(2), which differs from PGA(2) only in that its electrophilic carbon is rendered unreactive through steric hindrance. Taken together, these data suggest a novel mechanism through which reactive prostanoids may activate nociceptive neurons independent of prostaglandin receptors.

Phenotypic alterations in type II alveolar epithelial cells in CD4+ T cell mediated lung inflammation

BACKGROUND

Although the contribution of alveolar type II epithelial cell (AEC II) activities in various aspects of respiratory immune regulation has become increasingly appreciated, our understanding of the contribution of AEC II transcriptosome in immunopathologic lung injury remains poorly understood. We have previously established a mouse model for chronic T cell-mediated pulmonary inflammation in which influenza hemagglutinin (HA) is expressed as a transgene in AEC II, in mice expressing a transgenic T cell receptor specific for a class II-restricted epitope of HA. Pulmonary inflammation in these mice occurs as a result of CD4+ T cell recognition of alveolar antigen. This model was utilized to assess the profile of inflammatory mediators expressed by alveolar epithelial target cells triggered by antigen-specific recognition in CD4+ T cell-mediated lung inflammation.

METHODS

We established a method that allows the flow cytometric negative selection and isolation of primary AEC II of high viability and purity. Genome wide transcriptional profiling was performed on mRNA isolated from AEC II isolated from healthy mice and from mice with acute and chronic CD4+ T cell-mediated pulmonary inflammation.

RESULTS

T cell-mediated inflammation was associated with expression of a broad array of cytokine and chemokine genes by AEC II cell, indicating a potential contribution of epithelial-derived chemoattractants to the inflammatory cell parenchymal infiltration. Morphologically, there was an increase in the size of activated epithelial cells, and on the molecular level, comparative transcriptome analyses of AEC II from inflamed versus normal lungs provide a detailed characterization of the specific inflammatory genes expressed in AEC II induced in the context of CD4+ T cell-mediated pneumonitis.

CONCLUSION

An important contribution of AEC II gene expression to the orchestration and regulation of interstitial pneumonitis is suggested by the panoply of inflammatory genes expressed by this cell population, and this may provide insight into the molecular pathogenesis of pulmonary inflammatory states. CD4+ T cell recognition of antigen presented by AEC II cells appears to be a potent trigger for activation of the alveolar cell inflammatory transcriptosome.

Glycosylation and annexin II cell surface translocation mediate airway epithelial wound repair

Glycosylation of cell surface proteins can regulate multiple cellular functions. We hypothesized that glycosylation and expression of glycoproteins after epithelial injury is important in mediating repair. We report the use of an in vitro culture model of human airway epithelial cells (1HAEo(-)) to identify mediators of epithelial repair. We characterized carbohydrate moieties associated with repair by their interaction with the lectin from Cicer arietinum, chickpea agglutinin (CPA). Using CPA, we identified changes in cell surface glycosylation during wound repair. Following mechanical wounding of confluent monolayers of 1HAEo(-) cells, CPA staining increases on the cell surface of groups of cells in proximity to the wound edge. Blocking the CPA carbohydrate ligand inhibited wound repair highlighting the role of the CPA carbohydrate ligand in epithelial repair. Annexin II (AII), a calcium-dependent, membrane-associated protein, was identified as a protein associated with the CPA ligand. By membrane protein biotinylation and immunodetection, we have shown that following mechanical wounding, the presentation of AII on the cell surface increases coordinate with repair. Cell surface AII accumulates in proximity to the wound. Furthermore, translocation of AII to the cell surface is N-glycosylation dependent. We are the first to demonstrate that following injury, N-glycosylation events and AII presentation on the cell surface of airway epithelial cells are important mediators in repair.