Aclidinium bromide abrogates allergen-induced hyperresponsiveness and reduces eosinophilia in murine model of airway inflammation

Abstract

Airway hyperresponsiveness and inflammation characterize the airways of individuals with asthma and chronic obstructive pulmonary disease (COPD). Hence, therapeutic approaches that attenuate such manifestations may offer promise in the management of these diseases. In the present study, we investigated whether a novel long-acting cholinergic antagonist, aclidinium bromide, modulates airway function and leukocyte trafficking in an Aspergillus fumigatus (Af)-induced murine model of asthma. Nebulized aclidinium (1 mg/ml) administration completely abrogated increases in methacholine-induced lung resistance in Af-exposed mice. Parallel assessment of dynamic compliance showed that aclidinium also completely restores methacholine-mediated decreases in naïve and Af-exposed mice. As evidenced by differential cell counts within bronchoalveolar lavage fluid, aclidinium also diminished (51 ± 4%) Af-induced airway eosinophil numbers with no significant change in other immune cell types. Further assessment of cytokine and total protein levels in bronchoalveolar lavage fluid showed that aclidinium had little effect on IL-4 or IL-6 levels in either Af-exposed or naïve mice but markedly decreased total protein levels in bronchoalveolar lavage fluid. These data suggest that aclidinium, a selective muscarinic antagonist, not only acts as a bronchodilator but could also act as an anti-inflammatory agent with potential clinical benefits in the treatment of COPD and asthma.

Introduction

Acetylcholine, a pivotal airway parasympathetic neurotransmitter, promotes airway smooth muscle shortening and mucus secretion in airways (Belmonte, 2005). As enhanced parasympathetic activity correlates with airway inflammation and hyperresponsiveness, the use of anticholinergics has been advocated to yield substantial therapeutic benefits in treatment of asthma and COPD. In human studies, the concomitant use of long-acting β₂ adrenergic agonists and long-acting muscarinic receptor antagonists provides clinically relevant improvements in bronchodilation and patient symptoms compared to treatment with either agent alone (Tashkin et al., 2008, van Noord et al., 2006). In addition to restoring airway function, the combination of a long-acting muscarinic receptor antagonist with a long-acting β₂ adrenergic agonist effectively decreases the rate of COPD exacerbations (Cazzola and Matera, 2008). In animal studies, such combinations substantially attenuate bronchoconstriction following a variety of challenges (Rossoni et al., 2007). Interestingly, even parameters independent of airway smooth muscle relaxation such as thromboxane A release were significantly altered by long-acting muscarinic receptor antagonists suggesting broader therapeutic benefits when used in conjunction with existing respiratory medications.

Among the five subtypes of muscarinic receptors (M₁–M₅), the M₃ receptors are localized in airway smooth muscle tissue and mediate vagal and methacholine-induced bronchoconstrictor responses (Coulson and Fryer, 2003). Accordingly, bronchodilation occurs by selective antagonism of airway localized M₃ receptors, while non-selective antagonism may also promote systemic blockade of M₂ receptors inducing unwarranted cardiovascular effects (Barnes, 2004). Aclidinium bromide, an inhaled cholinergic antagonist with sub-nano molar affinity for all muscarinic receptors, manifests a high kinetic selectivity for the M₃ receptor (Gavalda et al., 2009b). In comparison to existing anti-muscarinic drugs including tiotropium, aclidinium undergoes rapid hydrolysis in human plasma, resulting in low and transient systemic exposure, diminishing the potential for class-related systemic side effects. In the present study, using a well-characterized murine model of allergen-induced airway hyperresponsiveness and inflammation, we studied the effect of aclidinium in modulating Aspergillus fumigatus (Af)-induced airway hyperresponsiveness. We also investigated the anti-inflammatory potential of aclidinium by measuring leukocyte numbers and cytokine levels in bronchoalveolar lavage fluid.