Isabella Bos

Inhibition of allergen-induced airway remodelling by tiotropium and budesonide: a comparison

Chronic inflammation in asthma and chronic obstructive pulmonary disease drives pathological structural remodelling of the airways. Using tiotropium bromide, acetylcholine was recently identified as playing a major regulatory role in airway smooth muscle remodelling in a guinea pig model of ongoing allergic asthma. The aim of the present study was to investigate other aspects of airway remodelling and to compare the effectiveness of tiotropium to the glucocorticosteroid budesonide. Ovalbumin-sensitised guinea pigs were challenged for 12 weeks with aerosolised ovalbumin. The ovalbumin induced airway smooth muscle thickening, hypercontractility of tracheal smooth muscle, increased pulmonary contractile protein (smooth-muscle myosin) abundance, mucous gland hypertrophy, an increase in mucin 5 subtypes A and C (MUC5AC)-positive goblet cell numbers and eosinophilia. It was reported previously that treatment with tiotropium inhibits airway smooth muscle thickening and contractile protein expression, and prevents tracheal hypercontractility. This study demonstrates that tiotropium also fully prevented allergen-induced mucous gland hypertrophy, and partially reduced the increase in MUC5AC-positive goblet cell numbers and eosinophil infiltration. Treatment with budesonide also prevented airway smooth muscle thickening, contractile protein expression, tracheal hypercontractility and mucous gland hypertrophy, and partially reduced MUC5AC-positive goblet cell numbers and eosinophilia. This study demonstrates that tiotropium and budesonide are similarly effective in inhibiting several aspects of airway remodelling, providing further evidence that the beneficial effects of tiotropium bromide might exceed those of bronchodilation.

Increased arginase activity contributes to airway remodelling in chronic allergic asthma

Airway remodelling, characterised by increased airway smooth muscle (ASM) mass, subepithelial fibrosis, goblet cell hyperplasia and mucus gland hypertrophy, is a feature of chronic asthma. Increased arginase activity could contribute to these features via increased formation of polyamines and l-proline downstream of the arginase product l-ornithine, and via reduced nitric oxide synthesis. Using the specific arginase inhitibor 2(S)-amino-6-boronohexanoic acid (ABH), we studied the role of arginase in airway remodelling using a guinea pig model of chronic asthma. Ovalbumin-sensitised guinea pigs were treated with ABH or PBS via inhalation before each of 12 weekly allergen or saline challenges, and indices of arginase activity, and airway remodelling, inflammation and responsiveness were studied 24 h after the final challenge. Pulmonary arginase activity of repeatedly allergen-challenged guinea pigs was increased. Allergen challenge also increased ASM mass and maximal contraction of denuded tracheal rings, which were prevented by ABH. ABH also attenuated allergen-induced pulmonary hydroxyproline (fibrosis) and putrescine, mucus gland hypertrophy, goblet cell hyperplasia, airway eosinophilia and interleukin-13, whereas an increased l-ornithine/l-citrulline ratio in the lung was normalised. Moreover, allergen-induced hyperresponsiveness of perfused tracheae was fully abrogated by ABH. These findings demonstrate that arginase is prominently involved in allergen-induced airway remodelling, inflammation and hyperresponsiveness in chronic asthma.

l-Arginine deficiency causes airway hyperresponsiveness after the late asthmatic reaction

Peroxynitrite has been shown to be crucially involved in airway hyperresponsiveness (AHR) after the late asthmatic reaction (LAR). Peroxynitrite production may result from simultaneous synthesis of nitric oxide (NO) and superoxide by inducible NO-synthase (iNOS) at low l-arginine concentrations. l-Arginine availability to iNOS is regulated by its cellular uptake, which can be inhibited by eosinophil-derived polycations and by arginase, which competes with iNOS for the common substrate. Using a guinea pig model of allergic asthma, we investigated whether aberrant l-arginine homeostasis could underlie peroxynitrite-mediated AHR after the LAR. After the LAR, arginase activity in the airways and eosinophil peroxidase release from bronchoalveolar lavage cells were increased. These changes were associated with a 2.0-fold AHR to methacholine as measured in isolated perfused tracheal preparations. AHR was reduced by exogenous l-arginine administration. Moreover, both the arginase inhibitor Nω-hydroxy-nor-l-arginine (nor-NOHA) and the polycation antagonist heparin normalised airway responsiveness. These effects were reversed by the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester (l-NAME), indicating that both agents reduced AHR by restoring bronchodilating NO production. In conclusion, in allergen-challenged guinea pigs, the AHR after the LAR is caused by arginase- and polycation-induced attenuation of l-arginine availability to iNOS, which may switch the enzyme to simultaneous production of superoxide and NO, and, consequently, peroxynitrite.

Muscarinic receptor subtype-specific effects on cigarette smoke-induced inflammation in mice

Cholinergic tone contributes to airflow obstruction in chronic obstructive pulmonary disease. Accordingly, anticholinergics are effective bronchodilators by blocking the muscarinic M3 receptor on airway smooth muscle. Recent evidence indicates that acetylcholine also contributes to airway inflammation. However, which muscarinic receptor subtype(s) regulates this process is unknown. In this study, the contribution of the M1, M2 and M3 receptor subtypes to cigarette smoke-induced airway inflammation was investigated by exposing muscarinic receptor subtype deficient mice to cigarette smoke for 4 days. In wild-type mice, cigarette smoke induced an increase in macrophages, neutrophils and lymphocytes in bronchoalveolar lavage fluid. Neutrophilic inflammation was higher in M1-/- and M2-/- mice compared to wild-type mice, but lower in M3-/- mice. Accordingly, the release of keratinocyte-derived chemokine (KC), monocyte chemotactic protein-1 and interleukin-6 was higher in M1-/- and M2-/- mice, and reduced in M3-/- mice. Markers of remodelling were not increased after cigarette smoke exposure. However, M3-/- mice had reduced expression of transforming growth factor-&bgr;1 and matrix proteins. Cigarette smoke-induced inflammatory cell recruitment and KC release were also prevented by the M3-receptor selective antagonist 1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP) in wild-type mice. Collectively, our data indicate a pro-inflammatory role for the M3 receptor in cigarette smoke-induced neutrophilia and cytokine release, yet an anti-inflammatory role for M1 and M2 receptors. Inhibition of the muscarinic M3 receptor prevents inflammation in response to cigarette smoke exposure in mice http://ow.ly/p7UdG