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A7158 - Muscarinic Receptor Stimulation Enhances Pathophysiological Phenotypes in Murine Model of COPD
Author Block: Y. Hamakawa1, A. Sato2, N. Tanabe3, K. Uemasu4, K. Hasegawa5, T. Mizutani1, S. Sato6, S. Muro7, T. Hirai8; 1Respiratory Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan, 2Respiratory Medicine, Kyoto University, Kyoto, Japan, 3Kyoto University Graduate School of Medicine, Kyoto, Japan, 4Kyoto University Graduate School of Medicine, Kyoto city, Japan, 5Respiratory medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan, 6Respiratory Medicine, Kyoto University Hospital, Kyoto, Japan, 7Respiratory Medicine, Kyoto Univ Hosp, Kyoto City, Japan, 8Dept of Resp Medicine, Kyoto Univ, Kyoto, Japan.
Rationale: Experimental studies have shown that functional alteration of muscarinic receptors (MR) is involved in lung inflammation and airway remodeling. However, much remains to be learned about the pathophysiological roles of MRs signaling in the pathogenesis of COPD. A recent clinical observation that an antagonist for MR type 3 ameliorates the decline of lung function in mild COPD, has led us to hypothesize that MR signaling might be activated consistently in COPD lungs and might be involved in lung parenchymal destruction. To test our hypothesis, the present study attempts to evaluate a murine model that mimics hyper-activation of MR in COPD lungs by administering acetylcholine analogues to lungs exposed to either cigarette smoke (CS) or elastase.
Methods: C57BL/6J male mice at age of 8-10 weeks were exposed to CS for 2 weeks or were injected low dose elastase (7.5 µ/body) intra-tracheally. In addition, those CS-exposed or elastase-exposed mice were treated intra-tracheally either with carbachol (acetylcholine analogue, 10 µg/kg) or saline. Inflammatory cell profiles in bronchoalveolar lavage fluid (BALF) were evaluated by flow cytometry. Lung function was measured by flexiVent® (SCIREQ Inc, Canada) and lung morphometry was performed using digital images of histological sections. Airspace enlargement was evaluated with the mean linear intercept (Lm). Destruction of alveolar septum was quantified with destructive index and ratio of abnormal alveolar attachments to total number of alveolar attachments (AA%). The heterogeneity of size and shape of peripheral airspaces was evaluated based on fractal analysis. Protease activity and inflammatory cytokines in BALF supernatant were evaluated.
Results: A combination of acetylcholine analogue and CS exposure synergistically enhanced neutrophilic inflammation in BALF. Histological analysis showed that this combinational exposure significantly increased AA% and the size heterogeneity of peripheral airspaces compared to lungs treated either with CS or acetylcholine analogue alone. The static compliance of carbachol injected group was increased compare to that of control group.
Conclusions: Those results were consistent with the idea that hyper-activation of MR-related pathways could exacerbate phenotypes in animal model of COPD. Acetylcholine can accelerate CS-induced lung inflammation and lung parenchymal destruction. In addition to bronchodilation, anti-cholinergic agent may exert clinical effects by ameliorating neutrophilic inflammation and further emphysematous destruction in COPD.