Airway Smooth Muscles Contractions in Metabolic Syndrome.

We studied contractile responses of isolated airway smooth muscle segments from rats with metabolic syndrome. Metabolic syndrome was induced in rats by high-fat and high-carbohydrate diet. It was shown that metabolic syndrome was associated with an increase of bronchoconstrictor action of cholinergic receptor activator carbacholine (0.1-100 µM) and a decrease of the dilatory effect of ß2-adrenoreceptor activator salbutamol (0.1-100 µM). The observed effects of agonists are epithelium-dependent. Disorders in contractile activity in the airway smooth muscles were accompanied by bronchial epithelium destruction, immune inflammation in the bronchial wall, muscular and peribronchial adipose tissue hypertrophy.

[Extracellular molecules controlling the contraction of airway smooth muscle and their potential contribution to bronchial hyperresponsiveness]. / La contractilité du muscle lisse des voies respiratoires est régulée par de nombreuses molécules extracellulaires qui pourraient contribuer à l'hyperréactivité bronchique.

INTRODUCTION: A significant portion of symptoms in some lung diseases results from an excessive constriction of airways due to the contraction of smooth muscle and bronchial hyperresponsiveness. A better understanding of the extracellular molecules that control smooth muscle contractility is necessary to identify the underlying causes of the problem. STATE OF KNOWLEDGE: Almost a hundred molecules, some of which newly identified, influence the contractility of airway smooth muscle. While some molecules activate the contraction, others activate the relaxation, thus acting directly as bronchoconstrictors and bronchodilators, respectively. Other molecules do not affect contraction directly but rather influence it indirectly by modifying the effect of bronchoconstrictors and bronchodilators. These are called bronchomodulators. Some of these bronchomodulators increase the contractile effect of bronchoconstrictors and could thus contribute to bronchial hyperresponsiveness. PROSPECTS: Considering the high number of molecules potentially involved, as well as the level of functional overlap between some of them, identifying the extracellular molecules responsible for excessive airway constriction in a patient is a major contemporary challenge.

MAP kinases mediate interleukin-13 effects on calcium signaling in human airway smooth muscle cells.

Interleukin-13 (IL-13) has been strongly implicated in the pathogenesis of allergic asthma through animal models that have shown that IL-13 is both necessary and sufficient to cause airway hyperresponsiveness (AHR). Airway smooth muscle (ASM) is a primary effector of AHR, and IL-13 increases the responsiveness of ASM, by increasing Ca(2+) release intracellularly, to bronchoconstrictors such as histamine. The mechanisms and signaling pathways mediating this effect are incompletely understood. We have investigated the pathways through which IL-13 regulates the Ca(2+) response to histamine in primary human ASM cell cultures. Functional IL-13 receptors were demonstrated by IL-13-mediated phosphorylation of signal transducer and activator of transcription 6 (STAT6) and mitogen-activated protein kinases (MAPKs). IL-13 increased Ca(2+) responses to histamine. The augmentation of Ca(2+) signaling was not affected by inhibition of STAT6 or p38 MAPK signaling but was prevented by concurrent inhibition of c-jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK) MAPKs. This inhibition did not affect the IL-13-induced increase in histamine receptors. We conclude that IL-13 induces potentiation of Ca(2+) responses to contractile agonists by affecting mechanisms downstream of receptors. JNK and ERK MAPKs modulate these mechanisms.

Synthesis, modeling, and biological evaluation of analogues of the semisynthetic brevetoxin antagonist beta-naphthoyl-brevetoxin.

Brevetoxins are neurotoxic compounds produced by the dinoflagellate Karenia brevis. Extensive blooms induce neurotoxic shellfish poisoning (NSP) and asthma-like symptoms in humans. beta-naphthoyl-brevetoxin, the first semisynthetic brevetoxin antagonist, has been defined as the lead compound in the investigation of the mechanisms of bronchoconstriction induced by inhaled brevetoxins and relaxation or reversal of those effects by selected derivatives. In pursuit of more potent and effective brevetoxin antagonists, a series of beta-naphthoyl-brevetoxin analogues have been synthesized. Activities were determined by competitive displacement of tritiated brevetoxin-3 from rat brain synaptosomes and by lung resistance measurements in sheep. Additionally, preliminary computational structural studies have been performed. All analogues bound to rat brain synaptosomes with affinities similar to beta-naphthoyl-brevetoxin but exhibited very different responses in sheep. The biological evaluations along with computational studies suggest that the brevetoxin binding site in rat brain synaptosome might be different from the ones in lung tissue and both steric and electrostatic factors contribute to the efficacy of brevetoxin antagonism.

Human bronchial epithelial cells express an active and inducible biosynthetic pathway for leukotrienes B4 and C4.

BACKGROUND: Human bronchial epithelial cells synthesize cyclooxygenase and 15-lipoxygenase products, but the 5-lipoxygenase (5-LO) pathway that generates the leukotriene (LT) family of bronchoconstrictor and pro-inflammatory mediators is thought to be restricted to leucocytes. OBJECTIVE: We hypothesized that human bronchial epithelial cells (HBECs) express a complete and active 5-LO pathway for the synthesis of LTB4 and LTC4, either constitutively or after stimulation. METHODS: Flow cytometry, RT-PCR, Western blotting, enzyme immunoassays and reverse-phase high-performance liquid chromatography were used to investigate constitutive and stimulated expression of 5-LO pathway enzymes and the synthesis of LTs B4 and C4 in primary HBECs and in the 16-HBE 14o- cell line. RESULTS: Constitutive mRNA and protein expression for 5-LO, 5-LO-activating protein (FLAP), LTA4 hydrolase and LTC4 synthase were demonstrated in primary HBECs and in the 16-HBE 14o- cell line. In 16-HBE 14o- cells, treatment with calcium ionophore A23187, bradykinin or LPS up-regulated the expression of these enzymes. The up-regulation of 5-LO was blocked by the anti-inflammatory glucocorticoid dexamethasone. Human bronchial epithelial cells were shown to generate bioactive LTs, with primary HBECs generating 11-fold more LTC4 and five-fold more LTB4 than 16-HBE 14o- cells. LT production was enhanced by ionophore treatment and blocked by the FLAP inhibitor MK-886. CONCLUSIONS: Expression of an active and inducible 5-LO pathway in HBEC suggests that damaged or inflamed bronchial epithelium may synthesize LTs that contribute directly to bronchoconstriction and leucocytosis in airway inflammation.

Mast cells can promote the development of multiple features of chronic asthma in mice.

Bronchial asthma, the most prevalent cause of significant respiratory morbidity in the developed world, typically is a chronic disorder associated with long-term changes in the airways. We developed a mouse model of chronic asthma that results in markedly increased numbers of airway mast cells, enhanced airway responses to methacholine or antigen, chronic inflammation including infiltration with eosinophils and lymphocytes, airway epithelial goblet cell hyperplasia, enhanced expression of the mucin genes Muc5ac and Muc5b, and increased levels of lung collagen. Using mast cell-deficient (Kit(W-sh/W-sh) and/or Kit(W/W-v)) mice engrafted with FcRgamma+/+ or FcRgamma-/- mast cells, we found that mast cells were required for the full development of each of these features of the model. However, some features also were expressed, although usually at less than wild-type levels, in mice whose mast cells lacked FcRgamma and therefore could not be activated by either antigen- and IgE-dependent aggregation of Fc epsilonRI or the binding of antigen-IgG1 immune complexes to Fc gammaRIII. These findings demonstrate that mast cells can contribute to the development of multiple features of chronic asthma in mice and identify both Fc Rgamma-dependent and Fc Rgamma-independent pathways of mast cell activation as important for the expression of key features of this asthma model.

Lung deposition of mannitol powder aerosol in healthy subjects.

Mannitol as a dry powder aerosol is used for bronchoprovocation testing and to enhance mucus clearance in people with excessive airway secretions. The dose and distribution of the deposited aerosol in the lung was investigated using fast single photon emission tomography (SPECT) imaging. Mannitol powder (3 microm particle size) was produced by spray drying and radiolabeled with (99m)Tc-DTPA. Approximately 60 mg of radiolabeled mannitol (containing 52-68 MBq of (99m)Tc-DTPA) was administered to 10 healthy subjects using the Inhalator dry powder inhaler (DPI), and SPECT images (1 min each) were collected. Thirteen percent to 31% of the dose of mannitol loaded in the inhaler deposited in the lungs and the deposited dose correlated positively with the peak inhalation air flow. The regional aerosol lung distribution, as expressed by the penetration index (i.e., ratio of peripheral to central deposition in the lung) varied from 0.31 to 0.88, which however showed no dependency on any flow parameters. The variation in response to the same dose of mannitol within the asthmatic population may in part be explained by these findings.

Elevated circulating adenosine level potentiates antigen-induced immediate bronchospasm and bronchoconstrictor mediator release in sensitized guinea pigs.

BACKGROUND: Adenosine causes bronchoconstriction in asthmatic patients, and it is also accepted that adenosine influences histamine release from activated human mast cells and basophils in vitro. OBJECTIVE: In this study we tested the hypothesis that adenosine potentiates both the airway narrowing and the release of bronchoconstrictor mediators induced by ovalbumin challenge in sensitized guinea pigs. METHODS: After ovalbumin sensitization, 4 groups were studied: control group, adenosine group (ADO), ovalbumin group (OA), and adenosine plus ovalbumin group (ADO + OA). Changes in airway resistance were assessed from continuously recorded pulmonary insuffilation pressure (PIP). The concentration of histamine, PGD2, and thromboxane B2 were determined from bronchoalveolar lavage fluids. RESULTS: Adenosine alone (6 mg/kg intravenously) did not influence baseline values of PIP and the mediator concentrations; however, ovalbumin (10 mg/kg intravenously) increased both the PIP and the levels of the measured mediators compared with the control and ADO groups. When ovalbumin challenge was preceded by adenosine administration, both PIP and mediator levels were significantly enhanced compared with values obtained after simple ovalbumin provocation (ADO + OA vs OA: P <.05). CONCLUSION: These results suggest that adenosine potentiates the airway narrowing induced by ovalbumin challenge and that this effect may develop through facilitation of the release of bronchoconstrictor mediators during the immediate airway response.

Pharmacology of airway smooth muscle.

Airway smooth muscle contributes to changes in airway caliber not only through the variations in its tone but also through its contribution to thickness of the airway wall. Until recently, most attention was paid to the agents that altered airway smooth muscle tone, their receptors, the signal transduction pathways they activated, and the mechanisms of contraction and relaxation themselves. Lately, the regulation of smooth muscle proliferation has received increasing attention, and, most recently, the possible role of smooth muscle as a source of inflammatory mediators has been recognized. Airway smooth muscle cells are now seen as playing an important interactive role with inflammatory and structural cells in the response to injury and repair of the airways.

Sputum eosinophilia is more closely associated with airway responsiveness to bradykinin than methacholine in asthma.

Hyperresponsiveness of the airways to various spasmogenic stimuli is a characteristic feature of bronchial asthma. However, the association between the different stimuli to which asthmatic airways are hyperresponsive and airways inflammation is not completely understood. We have investigated the relationship between airway inflammation and airway hyperresponsiveness in asthma, as assessed by bronchoprovocation tests to methacholine and bradykinin, two well defined bronchoconstrictor agonists. Sputum induction by hypertonic saline and methacholine and bradykinin challenges were performed in 14 nonsmoking subjects with mild-to-moderate asthma. Airway responsiveness to either agonist did not correlate with sputum neutrophils, lymphocytes, and macrophages. Whilst the absolute number of eosinophilia failed to be significantly related to methacholine responsiveness (r=-0.47; p=0.09), it correlated markedly and significantly with provocative concentration of methacholine causing a 20% fall in forced expiratory volume in one second (r=0.72; p<0.01). When expressed as % of total cell counts, sputum eosinophils correlated with both types of responsiveness (r=-056; p=0.04 and r=-0.76, p<0.001, respectively). Although the concentration of eosinophil cationic protein (ECP) in the sputum correlated with the absolute numbers of eosinophils (r=0.62; p<0.02), no correlation was found between ECP levels and the airway responsiveness to any of the agonists tested. In subjects with mild-to-moderate asthma, airway responsiveness to bradykinin is more strongly associated with the magnitude of eosinophilic inflammation in the airways than methacholine. This finding underlines the selectivity of diverse agonists in assessing airway hyperresponsiveness and cellular inflammation in asthma.